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 $58.69   5.329%   $61.8176   $61.82   $61.80   $61.80  
  Purchase #2 $241.84   3.292%   $249.8014   $249.80   $249.80   $249.80  
  Purchase #3 $21.28   11.781%   $23.787   $23.79   $23.80   $23.80  
  Purchase #4 $154.91   10.867%   $171.7441   $171.74   $171.75   $171.70  
  Purchase #5 $97.44   8.244%   $105.473   $105.47   $105.45   $105.50  
  Purchase #6 $59.57   4.642%   $62.3352   $62.34   $62.35   $62.30  
  Purchase #7 $177.50   13.756%   $201.9169   $201.92   $201.90   $201.90  
  7 purchase totals = $811.23       $876.8752   $876.88   $876.85   $876.80