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 $89.88   4.721%   $94.1232   $94.12   $94.10   $94.10  
  Purchase #2 $128.44   3.479%   $132.9084   $132.91   $132.90   $132.90  
  Purchase #3 $26.54   4.500%   $27.7343   $27.73   $27.75   $27.70  
  Purchase #4 $121.92   7.422%   $130.9689   $130.97   $130.95   $131.00  
  Purchase #5 $246.60   4.736%   $258.279   $258.28   $258.30   $258.30  
  Purchase #6 $137.33   10.580%   $151.8595   $151.86   $151.85   $151.90  
  Purchase #7 $199.96   13.574%   $227.1026   $227.10   $227.10   $227.10  
  7 purchase totals = $950.67       $1,022.9759   $1,022.97   $1,022.95   $1,023.00