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 $56.61   11.142%   $62.9175   $62.92   $62.90   $62.90  
  Purchase #2 $124.64   7.254%   $133.6814   $133.68   $133.70   $133.70  
  Purchase #3 $67.69   13.823%   $77.0468   $77.05   $77.05   $77.00  
  Purchase #4 $82.77   10.342%   $91.3301   $91.33   $91.35   $91.30  
  Purchase #5 $118.82   12.555%   $133.7379   $133.74   $133.75   $133.70  
  Purchase #6 $63.69   6.802%   $68.0222   $68.02   $68.00   $68.00  
  Purchase #7 $201.82   13.447%   $228.9587   $228.96   $228.95   $229.00  
  7 purchase totals = $716.04       $795.6946   $795.70   $795.70   $795.60