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 $58.67   12.633%   $66.0818   $66.08   $66.10   $66.10  
  Purchase #2 $26.44   12.213%   $29.6691   $29.67   $29.65   $29.70  
  Purchase #3 $181.79   9.594%   $199.2309   $199.23   $199.25   $199.20  
  Purchase #4 $61.30   3.758%   $63.6037   $63.60   $63.60   $63.60  
  Purchase #5 $99.78   3.733%   $103.5048   $103.50   $103.50   $103.50  
  Purchase #6 $141.25   5.306%   $148.7447   $148.74   $148.75   $148.70  
  Purchase #7 $154.50   4.723%   $161.797   $161.80   $161.80   $161.80  
  7 purchase totals = $723.73       $772.6320   $772.62   $772.65   $772.60