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 $75.57   9.123%   $82.4643   $82.46   $82.45   $82.50  
  Purchase #2 $244.89   11.296%   $272.5528   $272.55   $272.55   $272.60  
  Purchase #3 $68.91   7.418%   $74.0217   $74.02   $74.00   $74.00  
  Purchase #4 $164.78   10.728%   $182.4576   $182.46   $182.45   $182.50  
  Purchase #5 $13.42   6.755%   $14.3265   $14.33   $14.35   $14.30  
  Purchase #6 $137.93   3.733%   $143.0789   $143.08   $143.10   $143.10  
  Purchase #7 $103.44   8.283%   $112.0079   $112.01   $112.00   $112.00  
  7 purchase totals = $808.94       $880.9097   $880.91   $880.90   $881.00