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 $225.85   3.157%   $232.9801   $232.98   $233.00   $233.00  
  Purchase #2 $148.55   10.777%   $164.5592   $164.56   $164.55   $164.60  
  Purchase #3 $156.80   11.709%   $175.1597   $175.16   $175.15   $175.20  
  Purchase #4 $28.60   5.466%   $30.1633   $30.16   $30.15   $30.20  
  Purchase #5 $132.69   8.504%   $143.974   $143.97   $143.95   $144.00  
  Purchase #6 $137.95   9.585%   $151.1725   $151.17   $151.15   $151.20  
  Purchase #7 $158.72   3.535%   $164.3308   $164.33   $164.35   $164.30  
  7 purchase totals = $989.16       $1,062.3396   $1,062.33   $1,062.30   $1,062.50