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 $50.86   3.458%   $52.6187   $52.62   $52.60   $52.60  
  Purchase #2 $153.79   3.730%   $159.5264   $159.53   $159.55   $159.50  
  Purchase #3 $117.73   13.557%   $133.6907   $133.69   $133.70   $133.70  
  Purchase #4 $238.95   4.771%   $250.3503   $250.35   $250.35   $250.40  
  Purchase #5 $141.83   12.792%   $159.9729   $159.97   $159.95   $160.00  
  Purchase #6 $95.64   8.757%   $104.0152   $104.02   $104.00   $104.00  
  Purchase #7 $153.49   3.871%   $159.4316   $159.43   $159.45   $159.40  
  7 purchase totals = $952.29       $1,019.6058   $1,019.61   $1,019.60   $1,019.60