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 $68.71   11.527%   $76.6302   $76.63   $76.65   $76.60  
  Purchase #2 $242.59   10.291%   $267.5549   $267.55   $267.55   $267.60  
  Purchase #3 $175.81   9.315%   $192.1867   $192.19   $192.20   $192.20  
  Purchase #4 $141.52   3.567%   $146.568   $146.57   $146.55   $146.60  
  Purchase #5 $215.85   11.108%   $239.8266   $239.83   $239.85   $239.80  
  Purchase #6 $161.31   9.452%   $176.557   $176.56   $176.55   $176.60  
  Purchase #7 $185.62   10.596%   $205.2883   $205.29   $205.30   $205.30  
  7 purchase totals = $1,191.41       $1,304.6117   $1,304.62   $1,304.65   $1,304.70