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 $60.60   12.803%   $68.3586   $68.36   $68.35   $68.40  
  Purchase #2 $26.38   8.768%   $28.693   $28.69   $28.70   $28.70  
  Purchase #3 $210.66   12.711%   $237.437   $237.44   $237.45   $237.40  
  Purchase #4 $126.94   8.555%   $137.7997   $137.80   $137.80   $137.80  
  Purchase #5 $146.25   6.281%   $155.436   $155.44   $155.45   $155.40  
  Purchase #6 $69.87   8.762%   $75.992   $75.99   $76.00   $76.00  
  Purchase #7 $111.65   9.339%   $122.077   $122.08   $122.10   $122.10  
  7 purchase totals = $752.35       $825.7933   $825.80   $825.85   $825.80