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 $235.25   13.635%   $267.3263   $267.33   $267.35   $267.30  
  Purchase #2 $44.88   4.643%   $46.9638   $46.96   $46.95   $47.00  
  Purchase #3 $64.47   6.641%   $68.7515   $68.75   $68.75   $68.80  
  Purchase #4 $246.74   6.395%   $262.519   $262.52   $262.50   $262.50  
  Purchase #5 $67.89   6.242%   $72.1277   $72.13   $72.15   $72.10  
  Purchase #6 $94.67   11.186%   $105.2598   $105.26   $105.25   $105.30  
  Purchase #7 $53.59   13.633%   $60.8959   $60.90   $60.90   $60.90  
  7 purchase totals = $807.49       $883.8440   $883.85   $883.85   $883.90