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 $59.68   8.730%   $64.8901   $64.89   $64.90   $64.90  
  Purchase #2 $245.31   11.401%   $273.2778   $273.28   $273.30   $273.30  
  Purchase #3 $88.90   11.330%   $98.9724   $98.97   $98.95   $99.00  
  Purchase #4 $203.40   11.460%   $226.7096   $226.71   $226.70   $226.70  
  Purchase #5 $193.33   9.212%   $211.1396   $211.14   $211.15   $211.10  
  Purchase #6 $217.85   7.496%   $234.18   $234.18   $234.20   $234.20  
  Purchase #7 $65.94   3.827%   $68.4635   $68.46   $68.45   $68.50  
  7 purchase totals = $1,074.41       $1,177.6330   $1,177.63   $1,177.65   $1,177.70