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 $243.85   6.808%   $260.4513   $260.45   $260.45   $260.50  
  Purchase #2 $227.98   8.165%   $246.5946   $246.59   $246.60   $246.60  
  Purchase #3 $238.73   6.720%   $254.7727   $254.77   $254.75   $254.80  
  Purchase #4 $62.77   8.386%   $68.0339   $68.03   $68.05   $68.00  
  Purchase #5 $122.94   9.226%   $134.2824   $134.28   $134.30   $134.30  
  Purchase #6 $82.68   3.504%   $85.5771   $85.58   $85.60   $85.60  
  Purchase #7 $250.70   12.639%   $282.386   $282.39   $282.40   $282.40  
  7 purchase totals = $1,229.65       $1,332.0980   $1,332.09   $1,332.15   $1,332.20