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 $203.94   10.327%   $225.0009   $225.00   $225.00   $225.00  
  Purchase #2 $85.38   11.165%   $94.9127   $94.91   $94.90   $94.90  
  Purchase #3 $97.54   4.237%   $101.6728   $101.67   $101.65   $101.70  
  Purchase #4 $49.92   4.134%   $51.9837   $51.98   $52.00   $52.00  
  Purchase #5 $25.60   4.173%   $26.6683   $26.67   $26.65   $26.70  
  Purchase #6 $89.70   10.533%   $99.1481   $99.15   $99.15   $99.10  
  Purchase #7 $132.85   13.163%   $150.337   $150.34   $150.35   $150.30  
  7 purchase totals = $684.93       $749.7235   $749.72   $749.70   $749.70