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 $215.87   9.649%   $236.6993   $236.70   $236.70   $236.70  
  Purchase #2 $102.86   3.586%   $106.5486   $106.55   $106.55   $106.50  
  Purchase #3 $56.95   4.152%   $59.3146   $59.31   $59.30   $59.30  
  Purchase #4 $187.39   12.781%   $211.3403   $211.34   $211.35   $211.30  
  Purchase #5 $73.63   3.166%   $75.9611   $75.96   $75.95   $76.00  
  Purchase #6 $93.60   8.194%   $101.2696   $101.27   $101.25   $101.30  
  Purchase #7 $25.62   11.470%   $28.5586   $28.56   $28.55   $28.60  
  7 purchase totals = $755.92       $819.6921   $819.69   $819.65   $819.70