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 $89.41   7.131%   $95.7858   $95.79   $95.80   $95.80  
  Purchase #2 $16.47   13.444%   $18.6842   $18.68   $18.70   $18.70  
  Purchase #3 $176.86   3.141%   $182.4152   $182.42   $182.40   $182.40  
  Purchase #4 $51.53   3.866%   $53.5221   $53.52   $53.50   $53.50  
  Purchase #5 $70.74   7.317%   $75.916   $75.92   $75.90   $75.90  
  Purchase #6 $65.49   10.522%   $72.3809   $72.38   $72.40   $72.40  
  Purchase #7 $208.51   7.753%   $224.6758   $224.68   $224.70   $224.70  
  7 purchase totals = $679.01       $723.3800   $723.39   $723.40   $723.40