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 $56.95   11.329%   $63.4019   $63.40   $63.40   $63.40  
  Purchase #2 $189.92   7.481%   $204.1279   $204.13   $204.15   $204.10  
  Purchase #3 $111.85   6.708%   $119.3529   $119.35   $119.35   $119.40  
  Purchase #4 $173.77   7.403%   $186.6342   $186.63   $186.65   $186.60  
  Purchase #5 $118.30   5.115%   $124.351   $124.35   $124.35   $124.40  
  Purchase #6 $112.48   12.172%   $126.1711   $126.17   $126.15   $126.20  
  Purchase #7 $226.81   4.593%   $237.2274   $237.23   $237.25   $237.20  
  7 purchase totals = $990.08       $1,061.2664   $1,061.26   $1,061.30   $1,061.30