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 $246.35   12.808%   $277.9025   $277.90   $277.90   $277.90  
  Purchase #2 $169.46   3.513%   $175.4131   $175.41   $175.40   $175.40  
  Purchase #3 $161.90   9.426%   $177.1607   $177.16   $177.15   $177.20  
  Purchase #4 $191.76   13.338%   $217.3369   $217.34   $217.35   $217.30  
  Purchase #5 $217.99   13.285%   $246.95   $246.95   $246.95   $247.00  
  Purchase #6 $111.31   7.144%   $119.262   $119.26   $119.25   $119.30  
  Purchase #7 $216.78   7.310%   $232.6266   $232.63   $232.65   $232.60  
  7 purchase totals = $1,315.55       $1,446.6518   $1,446.65   $1,446.65   $1,446.70