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 $118.89   9.216%   $129.8469   $129.85   $129.85   $129.80  
  Purchase #2 $25.89   3.874%   $26.893   $26.89   $26.90   $26.90  
  Purchase #3 $155.76   13.324%   $176.5135   $176.51   $176.50   $176.50  
  Purchase #4 $94.33   3.371%   $97.5099   $97.51   $97.50   $97.50  
  Purchase #5 $48.61   12.757%   $54.8112   $54.81   $54.80   $54.80  
  Purchase #6 $207.89   8.191%   $224.9183   $224.92   $224.90   $224.90  
  Purchase #7 $87.73   6.394%   $93.3395   $93.34   $93.35   $93.30  
  7 purchase totals = $739.10       $803.8323   $803.83   $803.80   $803.70