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 $86.90   12.869%   $98.0832   $98.08   $98.10   $98.10  
  Purchase #2 $205.98   3.845%   $213.8999   $213.90   $213.90   $213.90  
  Purchase #3 $156.44   6.709%   $166.9356   $166.94   $166.95   $166.90  
  Purchase #4 $224.30   11.785%   $250.7338   $250.73   $250.75   $250.70  
  Purchase #5 $25.84   8.216%   $27.963   $27.96   $27.95   $28.00  
  Purchase #6 $93.66   12.867%   $105.7112   $105.71   $105.70   $105.70  
  Purchase #7 $113.63   4.268%   $118.4797   $118.48   $118.50   $118.50  
  7 purchase totals = $906.75       $981.8064   $981.80   $981.85   $981.80