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 $227.61   8.533%   $247.032   $247.03   $247.05   $247.00  
  Purchase #2 $157.38   5.403%   $165.8832   $165.88   $165.90   $165.90  
  Purchase #3 $178.50   13.648%   $202.8617   $202.86   $202.85   $202.90  
  Purchase #4 $118.34   6.485%   $126.0143   $126.01   $126.00   $126.00  
  Purchase #5 $131.46   5.238%   $138.3459   $138.35   $138.35   $138.30  
  Purchase #6 $231.53   10.677%   $256.2505   $256.25   $256.25   $256.30  
  Purchase #7 $220.99   5.355%   $232.824   $232.82   $232.80   $232.80  
  7 purchase totals = $1,265.81       $1,369.2116   $1,369.20   $1,369.20   $1,369.20