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 $110.69   3.186%   $114.2166   $114.22   $114.20   $114.20  
  Purchase #2 $17.56   6.662%   $18.7298   $18.73   $18.75   $18.70  
  Purchase #3 $210.29   3.243%   $217.1097   $217.11   $217.10   $217.10  
  Purchase #4 $155.88   3.306%   $161.0334   $161.03   $161.05   $161.00  
  Purchase #5 $83.81   9.689%   $91.9304   $91.93   $91.95   $91.90  
  Purchase #6 $174.48   4.859%   $182.958   $182.96   $182.95   $183.00  
  Purchase #7 $200.32   12.234%   $224.8271   $224.83   $224.85   $224.80  
  7 purchase totals = $953.03       $1,010.8050   $1,010.81   $1,010.85   $1,010.70