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 $244.75   6.234%   $260.0077   $260.01   $260.00   $260.00  
  Purchase #2 $171.68   12.108%   $192.467   $192.47   $192.45   $192.50  
  Purchase #3 $72.99   10.812%   $80.8817   $80.88   $80.90   $80.90  
  Purchase #4 $73.59   7.161%   $78.8598   $78.86   $78.85   $78.90  
  Purchase #5 $227.74   11.302%   $253.4792   $253.48   $253.50   $253.50  
  Purchase #6 $207.89   11.590%   $231.9845   $231.98   $232.00   $232.00  
  Purchase #7 $141.62   9.250%   $154.7199   $154.72   $154.70   $154.70  
  7 purchase totals = $1,140.26       $1,252.3998   $1,252.40   $1,252.40   $1,252.50