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 $215.34   9.426%   $235.6379   $235.64   $235.65   $235.60  
  Purchase #2 $121.53   4.306%   $126.7631   $126.76   $126.75   $126.80  
  Purchase #3 $23.68   12.244%   $26.5794   $26.58   $26.60   $26.60  
  Purchase #4 $61.44   7.459%   $66.0228   $66.02   $66.00   $66.00  
  Purchase #5 $96.48   3.351%   $99.713   $99.71   $99.70   $99.70  
  Purchase #6 $245.79   9.151%   $268.2822   $268.28   $268.30   $268.30  
  Purchase #7 $70.75   10.601%   $78.2502   $78.25   $78.25   $78.30  
  7 purchase totals = $835.01       $901.2486   $901.24   $901.25   $901.30