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 $210.44   10.236%   $231.9806   $231.98   $232.00   $232.00  
  Purchase #2 $98.47   9.313%   $107.6405   $107.64   $107.65   $107.60  
  Purchase #3 $53.93   9.261%   $58.9245   $58.92   $58.90   $58.90  
  Purchase #4 $216.88   10.297%   $239.2121   $239.21   $239.20   $239.20  
  Purchase #5 $136.94   12.289%   $153.7686   $153.77   $153.75   $153.80  
  Purchase #6 $102.42   5.108%   $107.6516   $107.65   $107.65   $107.70  
  Purchase #7 $65.62   5.823%   $69.4411   $69.44   $69.45   $69.40  
  7 purchase totals = $884.70       $968.6190   $968.61   $968.60   $968.60