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 $213.41   11.307%   $237.5403   $237.54   $237.55   $237.50  
  Purchase #2 $141.53   12.799%   $159.6444   $159.64   $159.65   $159.60  
  Purchase #3 $231.87   6.169%   $246.1741   $246.17   $246.15   $246.20  
  Purchase #4 $29.69   10.380%   $32.7718   $32.77   $32.75   $32.80  
  Purchase #5 $199.53   3.242%   $205.9988   $206.00   $206.00   $206.00  
  Purchase #6 $210.72   10.280%   $232.382   $232.38   $232.40   $232.40  
  Purchase #7 $97.50   4.382%   $101.7725   $101.77   $101.75   $101.80  
  7 purchase totals = $1,124.25       $1,216.2839   $1,216.27   $1,216.25   $1,216.30