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 $92.53   5.211%   $97.3517   $97.35   $97.35   $97.40  
  Purchase #2 $166.26   4.158%   $173.1731   $173.17   $173.15   $173.20  
  Purchase #3 $152.38   3.790%   $158.1552   $158.16   $158.15   $158.20  
  Purchase #4 $179.72   9.170%   $196.2003   $196.20   $196.20   $196.20  
  Purchase #5 $157.26   13.143%   $177.9287   $177.93   $177.95   $177.90  
  Purchase #6 $140.97   6.138%   $149.6227   $149.62   $149.60   $149.60  
  Purchase #7 $104.90   12.122%   $117.616   $117.62   $117.60   $117.60  
  7 purchase totals = $994.02       $1,070.0477   $1,070.05   $1,070.00   $1,070.10