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 $34.95   4.376%   $36.4794   $36.48   $36.50   $36.50  
  Purchase #2 $89.64   13.473%   $101.7172   $101.72   $101.70   $101.70  
  Purchase #3 $153.29   8.223%   $165.895   $165.90   $165.90   $165.90  
  Purchase #4 $174.43   4.732%   $182.684   $182.68   $182.70   $182.70  
  Purchase #5 $203.62   4.773%   $213.3388   $213.34   $213.35   $213.30  
  Purchase #6 $53.54   6.580%   $57.0629   $57.06   $57.05   $57.10  
  Purchase #7 $41.42   12.774%   $46.711   $46.71   $46.70   $46.70  
  7 purchase totals = $750.89       $803.8883   $803.89   $803.90   $803.90