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 $66.67   7.149%   $71.4362   $71.44   $71.45   $71.40  
  Purchase #2 $102.84   13.572%   $116.7974   $116.80   $116.80   $116.80  
  Purchase #3 $151.62   7.540%   $163.0521   $163.05   $163.05   $163.10  
  Purchase #4 $157.67   6.257%   $167.5354   $167.54   $167.55   $167.50  
  Purchase #5 $87.47   9.167%   $95.4884   $95.49   $95.50   $95.50  
  Purchase #6 $239.29   11.341%   $266.4279   $266.43   $266.45   $266.40  
  Purchase #7 $169.26   5.831%   $179.1296   $179.13   $179.15   $179.10  
  7 purchase totals = $974.82       $1,059.8670   $1,059.88   $1,059.95   $1,059.80