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 $81.95   11.706%   $91.5431   $91.54   $91.55   $91.50  
  Purchase #2 $44.51   12.287%   $49.9789   $49.98   $50.00   $50.00  
  Purchase #3 $71.46   8.554%   $77.5727   $77.57   $77.55   $77.60  
  Purchase #4 $207.89   12.585%   $234.053   $234.05   $234.05   $234.10  
  Purchase #5 $54.42   10.332%   $60.0427   $60.04   $60.05   $60.00  
  Purchase #6 $225.69   11.345%   $251.2945   $251.29   $251.30   $251.30  
  Purchase #7 $97.26   6.416%   $103.5002   $103.50   $103.50   $103.50  
  7 purchase totals = $783.18       $867.9851   $867.97   $868.00   $868.00