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 $43.42   12.123%   $48.6838   $48.68   $48.70   $48.70  
  Purchase #2 $78.78   11.259%   $87.6498   $87.65   $87.65   $87.60  
  Purchase #3 $13.47   12.653%   $15.1744   $15.17   $15.15   $15.20  
  Purchase #4 $239.76   9.435%   $262.3814   $262.38   $262.40   $262.40  
  Purchase #5 $108.85   13.272%   $123.2966   $123.30   $123.30   $123.30  
  Purchase #6 $172.43   12.126%   $193.3389   $193.34   $193.35   $193.30  
  Purchase #7 $65.87   12.665%   $74.2124   $74.21   $74.20   $74.20  
  7 purchase totals = $722.58       $804.7373   $804.73   $804.75   $804.70