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 $55.46   12.756%   $62.5345   $62.53   $62.55   $62.50  
  Purchase #2 $236.59   12.415%   $265.9626   $265.96   $265.95   $266.00  
  Purchase #3 $183.34   12.354%   $205.9898   $205.99   $206.00   $206.00  
  Purchase #4 $157.51   5.869%   $166.7543   $166.75   $166.75   $166.80  
  Purchase #5 $236.70   8.502%   $256.8242   $256.82   $256.80   $256.80  
  Purchase #6 $176.38   9.618%   $193.3442   $193.34   $193.35   $193.30  
  Purchase #7 $81.53   12.111%   $91.4041   $91.40   $91.40   $91.40  
  7 purchase totals = $1,127.51       $1,242.8137   $1,242.79   $1,242.80   $1,242.80