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 $171.51   6.255%   $182.238   $182.24   $182.25   $182.20  
  Purchase #2 $30.59   9.823%   $33.5949   $33.59   $33.60   $33.60  
  Purchase #3 $219.53   6.578%   $233.9707   $233.97   $233.95   $234.00  
  Purchase #4 $52.29   13.329%   $59.2597   $59.26   $59.25   $59.30  
  Purchase #5 $232.55   13.271%   $263.4117   $263.41   $263.40   $263.40  
  Purchase #6 $14.42   3.309%   $14.8972   $14.90   $14.90   $14.90  
  Purchase #7 $165.84   5.512%   $174.9811   $174.98   $175.00   $175.00  
  7 purchase totals = $886.73       $962.3533   $962.35   $962.35   $962.40