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 $94.81   3.201%   $97.8449   $97.84   $97.85   $97.80  
  Purchase #2 $124.39   5.788%   $131.5897   $131.59   $131.60   $131.60  
  Purchase #3 $226.46   9.872%   $248.8161   $248.82   $248.80   $248.80  
  Purchase #4 $151.27   5.706%   $159.9015   $159.90   $159.90   $159.90  
  Purchase #5 $204.85   5.541%   $216.2007   $216.20   $216.20   $216.20  
  Purchase #6 $225.71   13.596%   $256.3975   $256.40   $256.40   $256.40  
  Purchase #7 $139.27   7.320%   $149.4646   $149.46   $149.45   $149.50  
  7 purchase totals = $1,166.76       $1,260.2150   $1,260.21   $1,260.20   $1,260.20