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 $156.95   9.158%   $171.3235   $171.32   $171.30   $171.30  
  Purchase #2 $211.84   13.504%   $240.4469   $240.45   $240.45   $240.40  
  Purchase #3 $57.53   4.420%   $60.0728   $60.07   $60.05   $60.10  
  Purchase #4 $169.72   6.206%   $180.2528   $180.25   $180.25   $180.30  
  Purchase #5 $173.67   11.509%   $193.6577   $193.66   $193.65   $193.70  
  Purchase #6 $193.48   6.576%   $206.2032   $206.20   $206.20   $206.20  
  Purchase #7 $30.98   7.204%   $33.2118   $33.21   $33.20   $33.20  
  7 purchase totals = $994.17       $1,085.1687   $1,085.16   $1,085.10   $1,085.20