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 $52.63   13.269%   $59.6135   $59.61   $59.60   $59.60  
  Purchase #2 $56.97   6.129%   $60.4617   $60.46   $60.45   $60.50  
  Purchase #3 $194.93   8.200%   $210.9143   $210.91   $210.90   $210.90  
  Purchase #4 $28.50   12.135%   $31.9585   $31.96   $31.95   $32.00  
  Purchase #5 $205.67   8.355%   $222.8537   $222.85   $222.85   $222.90  
  Purchase #6 $24.29   10.760%   $26.9036   $26.90   $26.90   $26.90  
  Purchase #7 $97.44   4.641%   $101.9622   $101.96   $101.95   $102.00  
  7 purchase totals = $660.43       $714.6675   $714.65   $714.60   $714.80