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 $246.87   7.643%   $265.7383   $265.74   $265.75   $265.70  
  Purchase #2 $199.94   4.639%   $209.2152   $209.22   $209.20   $209.20  
  Purchase #3 $88.28   4.688%   $92.4186   $92.42   $92.40   $92.40  
  Purchase #4 $231.90   5.339%   $244.2811   $244.28   $244.30   $244.30  
  Purchase #5 $59.30   3.710%   $61.5   $61.50   $61.50   $61.50  
  Purchase #6 $47.48   12.803%   $53.5589   $53.56   $53.55   $53.60  
  Purchase #7 $234.28   9.604%   $256.7803   $256.78   $256.80   $256.80  
  7 purchase totals = $1,108.05       $1,183.4924   $1,183.50   $1,183.50   $1,183.50