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 $61.40   13.815%   $69.8824   $69.88   $69.90   $69.90  
  Purchase #2 $84.84   7.575%   $91.2666   $91.27   $91.25   $91.30  
  Purchase #3 $235.79   13.862%   $268.4752   $268.48   $268.50   $268.50  
  Purchase #4 $55.70   10.469%   $61.5312   $61.53   $61.55   $61.50  
  Purchase #5 $28.51   11.873%   $31.895   $31.90   $31.90   $31.90  
  Purchase #6 $197.84   11.473%   $220.5382   $220.54   $220.55   $220.50  
  Purchase #7 $95.42   6.241%   $101.3752   $101.38   $101.40   $101.40  
  7 purchase totals = $759.50       $844.9638   $844.98   $845.05   $845.00