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 $131.65   7.584%   $141.6343   $141.63   $141.65   $141.60  
  Purchase #2 $201.38   9.143%   $219.7922   $219.79   $219.80   $219.80  
  Purchase #3 $118.37   7.216%   $126.9116   $126.91   $126.90   $126.90  
  Purchase #4 $160.83   7.516%   $172.918   $172.92   $172.90   $172.90  
  Purchase #5 $243.39   12.744%   $274.4076   $274.41   $274.40   $274.40  
  Purchase #6 $58.87   10.389%   $64.986   $64.99   $65.00   $65.00  
  Purchase #7 $171.69   9.528%   $188.0486   $188.05   $188.05   $188.00  
  7 purchase totals = $1,086.18       $1,188.6983   $1,188.70   $1,188.70   $1,188.60