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 $81.54   8.455%   $88.4342   $88.43   $88.45   $88.40  
  Purchase #2 $26.98   13.865%   $30.7208   $30.72   $30.70   $30.70  
  Purchase #3 $102.77   10.225%   $113.2782   $113.28   $113.30   $113.30  
  Purchase #4 $150.33   8.382%   $162.9307   $162.93   $162.95   $162.90  
  Purchase #5 $157.70   4.776%   $165.2318   $165.23   $165.25   $165.20  
  Purchase #6 $49.49   6.621%   $52.7667   $52.77   $52.75   $52.80  
  Purchase #7 $169.33   7.646%   $182.277   $182.28   $182.30   $182.30  
  7 purchase totals = $738.14       $795.6394   $795.64   $795.70   $795.60