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 $67.98   11.501%   $75.7984   $75.80   $75.80   $75.80  
  Purchase #2 $97.93   13.632%   $111.2798   $111.28   $111.30   $111.30  
  Purchase #3 $24.38   12.584%   $27.448   $27.45   $27.45   $27.40  
  Purchase #4 $225.62   6.798%   $240.9576   $240.96   $240.95   $241.00  
  Purchase #5 $26.55   11.484%   $29.599   $29.60   $29.60   $29.60  
  Purchase #6 $29.90   12.505%   $33.639   $33.64   $33.65   $33.60  
  Purchase #7 $198.65   3.869%   $206.3358   $206.34   $206.35   $206.30  
  7 purchase totals = $671.01       $725.0576   $725.07   $725.10   $725.00