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 $52.95   11.318%   $58.9429   $58.94   $58.95   $58.90  
  Purchase #2 $138.33   12.521%   $155.6503   $155.65   $155.65   $155.70  
  Purchase #3 $86.37   9.574%   $94.6391   $94.64   $94.65   $94.60  
  Purchase #4 $248.29   12.416%   $279.1177   $279.12   $279.10   $279.10  
  Purchase #5 $89.71   6.288%   $95.351   $95.35   $95.35   $95.40  
  Purchase #6 $118.45   6.844%   $126.5567   $126.56   $126.55   $126.60  
  Purchase #7 $92.38   4.505%   $96.5417   $96.54   $96.55   $96.50  
  7 purchase totals = $826.48       $906.7994   $906.80   $906.80   $906.80