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 $98.36   6.517%   $104.7701   $104.77   $104.75   $104.80  
  Purchase #2 $209.47   3.430%   $216.6548   $216.65   $216.65   $216.70  
  Purchase #3 $171.39   6.464%   $182.4686   $182.47   $182.45   $182.50  
  Purchase #4 $152.93   4.843%   $160.3364   $160.34   $160.35   $160.30  
  Purchase #5 $235.32   10.212%   $259.3509   $259.35   $259.35   $259.40  
  Purchase #6 $236.29   12.301%   $265.356   $265.36   $265.35   $265.40  
  Purchase #7 $148.31   13.768%   $168.7293   $168.73   $168.75   $168.70  
  7 purchase totals = $1,252.07       $1,357.6661   $1,357.67   $1,357.65   $1,357.80