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 $175.65   4.355%   $183.2996   $183.30   $183.30   $183.30  
  Purchase #2 $228.87   3.254%   $236.3174   $236.32   $236.30   $236.30  
  Purchase #3 $94.87   7.441%   $101.9293   $101.93   $101.95   $101.90  
  Purchase #4 $148.90   9.865%   $163.589   $163.59   $163.60   $163.60  
  Purchase #5 $217.54   8.204%   $235.387   $235.39   $235.40   $235.40  
  Purchase #6 $82.82   4.722%   $86.7308   $86.73   $86.75   $86.70  
  Purchase #7 $242.89   3.404%   $251.158   $251.16   $251.15   $251.20  
  7 purchase totals = $1,191.54       $1,258.4111   $1,258.42   $1,258.45   $1,258.40