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 $136.88   3.769%   $142.039   $142.04   $142.05   $142.00  
  Purchase #2 $76.34   11.208%   $84.8962   $84.90   $84.90   $84.90  
  Purchase #3 $235.53   4.443%   $245.9946   $245.99   $246.00   $246.00  
  Purchase #4 $205.41   10.816%   $227.6271   $227.63   $227.65   $227.60  
  Purchase #5 $236.79   4.570%   $247.6113   $247.61   $247.60   $247.60  
  Purchase #6 $55.51   4.659%   $58.0962   $58.10   $58.10   $58.10  
  Purchase #7 $244.27   6.824%   $260.939   $260.94   $260.95   $260.90  
  7 purchase totals = $1,190.73       $1,267.2034   $1,267.21   $1,267.25   $1,267.10