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 $42.46   11.815%   $47.4766   $47.48   $47.50   $47.50  
  Purchase #2 $206.51   9.587%   $226.3081   $226.31   $226.30   $226.30  
  Purchase #3 $214.33   12.605%   $241.3463   $241.35   $241.35   $241.30  
  Purchase #4 $45.79   6.507%   $48.7696   $48.77   $48.75   $48.80  
  Purchase #5 $199.86   6.509%   $212.8689   $212.87   $212.85   $212.90  
  Purchase #6 $197.54   7.344%   $212.0473   $212.05   $212.05   $212.00  
  Purchase #7 $30.44   12.792%   $34.3339   $34.33   $34.35   $34.30  
  7 purchase totals = $936.93       $1,023.1507   $1,023.16   $1,023.15   $1,023.10