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 $76.32   10.871%   $84.6167   $84.62   $84.60   $84.60  
  Purchase #2 $202.97   3.645%   $210.3683   $210.37   $210.35   $210.40  
  Purchase #3 $239.84   8.612%   $260.495   $260.50   $260.50   $260.50  
  Purchase #4 $117.60   13.596%   $133.5889   $133.59   $133.60   $133.60  
  Purchase #5 $52.44   3.109%   $54.0704   $54.07   $54.05   $54.10  
  Purchase #6 $47.30   5.749%   $50.0193   $50.02   $50.00   $50.00  
  Purchase #7 $212.95   4.333%   $222.1771   $222.18   $222.20   $222.20  
  7 purchase totals = $949.42       $1,015.3357   $1,015.35   $1,015.30   $1,015.40