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 $246.62   6.709%   $263.1657   $263.17   $263.15   $263.20  
  Purchase #2 $198.72   9.350%   $217.3003   $217.30   $217.30   $217.30  
  Purchase #3 $195.40   4.721%   $204.6248   $204.62   $204.60   $204.60  
  Purchase #4 $43.71   11.226%   $48.6169   $48.62   $48.60   $48.60  
  Purchase #5 $149.55   13.481%   $169.7108   $169.71   $169.70   $169.70  
  Purchase #6 $85.49   8.119%   $92.4309   $92.43   $92.45   $92.40  
  Purchase #7 $127.26   6.354%   $135.3461   $135.35   $135.35   $135.30  
  7 purchase totals = $1,046.75       $1,131.1955   $1,131.20   $1,131.15   $1,131.10