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 $41.45   7.673%   $44.6305   $44.63   $44.65   $44.60  
  Purchase #2 $83.43   9.321%   $91.2065   $91.21   $91.20   $91.20  
  Purchase #3 $59.41   4.497%   $62.0817   $62.08   $62.10   $62.10  
  Purchase #4 $131.61   6.363%   $139.9843   $139.98   $140.00   $140.00  
  Purchase #5 $85.50   5.127%   $89.8836   $89.88   $89.90   $89.90  
  Purchase #6 $180.50   12.235%   $202.5842   $202.58   $202.60   $202.60  
  Purchase #7 $132.53   4.206%   $138.1042   $138.10   $138.10   $138.10  
  7 purchase totals = $714.43       $768.4750   $768.46   $768.55   $768.50