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 $78.46   8.337%   $85.0012   $85.00   $85.00   $85.00  
  Purchase #2 $210.97   6.492%   $224.6662   $224.67   $224.65   $224.70  
  Purchase #3 $81.63   13.854%   $92.939   $92.94   $92.95   $92.90  
  Purchase #4 $69.83   4.501%   $72.973   $72.97   $72.95   $73.00  
  Purchase #5 $45.94   4.560%   $48.0349   $48.03   $48.05   $48.00  
  Purchase #6 $114.63   8.822%   $124.7427   $124.74   $124.75   $124.70  
  Purchase #7 $126.83   4.157%   $132.1023   $132.10   $132.10   $132.10  
  7 purchase totals = $728.29       $780.4593   $780.45   $780.45   $780.40