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 $57.69   12.282%   $64.7755   $64.78   $64.80   $64.80  
  Purchase #2 $60.74   7.678%   $65.4036   $65.40   $65.40   $65.40  
  Purchase #3 $213.92   8.874%   $232.9033   $232.90   $232.90   $232.90  
  Purchase #4 $27.57   8.576%   $29.9344   $29.93   $29.95   $29.90  
  Purchase #5 $245.96   10.586%   $271.9973   $272.00   $272.00   $272.00  
  Purchase #6 $22.93   12.729%   $25.8488   $25.85   $25.85   $25.80  
  Purchase #7 $96.43   5.153%   $101.399   $101.40   $101.40   $101.40  
  7 purchase totals = $725.24       $792.2619   $792.26   $792.30   $792.20