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 $47.29   13.381%   $53.6179   $53.62   $53.60   $53.60  
  Purchase #2 $178.91   6.721%   $190.9345   $190.93   $190.95   $190.90  
  Purchase #3 $104.42   3.744%   $108.3295   $108.33   $108.35   $108.30  
  Purchase #4 $74.69   13.679%   $84.9068   $84.91   $84.90   $84.90  
  Purchase #5 $41.69   7.348%   $44.7534   $44.75   $44.75   $44.80  
  Purchase #6 $219.73   11.726%   $245.4955   $245.50   $245.50   $245.50  
  Purchase #7 $65.47   12.218%   $73.4691   $73.47   $73.45   $73.50  
  7 purchase totals = $732.20       $801.5067   $801.51   $801.50   $801.50