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 $86.34   13.457%   $97.9588   $97.96   $97.95   $98.00  
  Purchase #2 $61.49   12.370%   $69.0963   $69.10   $69.10   $69.10  
  Purchase #3 $113.62   4.299%   $118.5045   $118.50   $118.50   $118.50  
  Purchase #4 $70.67   12.641%   $79.6034   $79.60   $79.60   $79.60  
  Purchase #5 $150.99   7.747%   $162.6872   $162.69   $162.70   $162.70  
  Purchase #6 $40.94   13.558%   $46.4906   $46.49   $46.50   $46.50  
  Purchase #7 $202.94   8.130%   $219.439   $219.44   $219.45   $219.40  
  7 purchase totals = $726.99       $793.7798   $793.78   $793.80   $793.80