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 $237.86   10.228%   $262.1883   $262.19   $262.20   $262.20  
  Purchase #2 $172.66   11.122%   $191.8632   $191.86   $191.85   $191.90  
  Purchase #3 $149.33   3.303%   $154.2624   $154.26   $154.25   $154.30  
  Purchase #4 $154.76   13.550%   $175.73   $175.73   $175.75   $175.70  
  Purchase #5 $28.82   5.856%   $30.5077   $30.51   $30.50   $30.50  
  Purchase #6 $69.52   7.110%   $74.4629   $74.46   $74.45   $74.50  
  Purchase #7 $53.30   3.774%   $55.3115   $55.31   $55.30   $55.30  
  7 purchase totals = $866.25       $944.3260   $944.32   $944.30   $944.40