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 $238.50   13.147%   $269.8556   $269.86   $269.85   $269.90  
  Purchase #2 $174.97   3.127%   $180.4413   $180.44   $180.45   $180.40  
  Purchase #3 $58.79   13.254%   $66.582   $66.58   $66.60   $66.60  
  Purchase #4 $82.58   12.767%   $93.123   $93.12   $93.10   $93.10  
  Purchase #5 $235.35   10.316%   $259.6287   $259.63   $259.65   $259.60  
  Purchase #6 $244.51   7.423%   $262.66   $262.66   $262.65   $262.70  
  Purchase #7 $119.53   11.240%   $132.9652   $132.97   $132.95   $133.00  
  7 purchase totals = $1,154.23       $1,265.2558   $1,265.26   $1,265.25   $1,265.30