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 $56.62   11.187%   $62.9541   $62.95   $62.95   $63.00  
  Purchase #2 $121.75   7.836%   $131.2903   $131.29   $131.30   $131.30  
  Purchase #3 $77.34   13.503%   $87.7832   $87.78   $87.80   $87.80  
  Purchase #4 $75.88   13.239%   $85.9258   $85.93   $85.95   $85.90  
  Purchase #5 $106.71   7.361%   $114.5649   $114.56   $114.55   $114.60  
  Purchase #6 $168.88   8.118%   $182.5897   $182.59   $182.60   $182.60  
  Purchase #7 $12.60   6.464%   $13.4145   $13.41   $13.40   $13.40  
  7 purchase totals = $619.78       $678.5225   $678.51   $678.55   $678.60