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 $41.81   13.164%   $47.3139   $47.31   $47.30   $47.30  
  Purchase #2 $226.53   11.156%   $251.8017   $251.80   $251.80   $251.80  
  Purchase #3 $14.57   6.355%   $15.4959   $15.50   $15.50   $15.50  
  Purchase #4 $66.37   10.612%   $73.4132   $73.41   $73.40   $73.40  
  Purchase #5 $214.68   7.403%   $230.5728   $230.57   $230.55   $230.60  
  Purchase #6 $132.39   7.788%   $142.7005   $142.70   $142.70   $142.70  
  Purchase #7 $250.40   3.862%   $260.0704   $260.07   $260.05   $260.10  
  7 purchase totals = $946.75       $1,021.3684   $1,021.36   $1,021.30   $1,021.40