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 $227.62   11.852%   $254.5975   $254.60   $254.60   $254.60  
  Purchase #2 $148.48   10.246%   $163.6933   $163.69   $163.70   $163.70  
  Purchase #3 $172.61   13.612%   $196.1057   $196.11   $196.10   $196.10  
  Purchase #4 $13.41   9.124%   $14.6335   $14.63   $14.65   $14.60  
  Purchase #5 $136.98   3.772%   $142.1469   $142.15   $142.15   $142.10  
  Purchase #6 $121.47   10.331%   $134.0191   $134.02   $134.00   $134.00  
  Purchase #7 $139.58   8.135%   $150.9348   $150.93   $150.95   $150.90  
  7 purchase totals = $960.15       $1,056.1308   $1,056.13   $1,056.15   $1,056.00