Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $236.94   8.843%   $257.8926   $257.89   $257.90   $257.90  
  Purchase #2 $239.93   8.598%   $260.5592   $260.56   $260.55   $260.60  
  Purchase #3 $96.43   5.771%   $101.995   $102.00   $102.00   $102.00  
  Purchase #4 $167.32   4.472%   $174.8026   $174.80   $174.80   $174.80  
  Purchase #5 $177.29   10.453%   $195.8221   $195.82   $195.80   $195.80  
  Purchase #6 $156.56   13.378%   $177.5046   $177.50   $177.50   $177.50  
  Purchase #7 $93.84   8.191%   $101.5264   $101.53   $101.55   $101.50  
  7 purchase totals = $1,168.31       $1,270.1025   $1,270.10   $1,270.10   $1,270.10