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 $183.70   10.579%   $203.1336   $203.13   $203.15   $203.10  
  Purchase #2 $164.48   9.530%   $180.1549   $180.15   $180.15   $180.20  
  Purchase #3 $240.99   5.545%   $254.3529   $254.35   $254.35   $254.40  
  Purchase #4 $44.70   10.509%   $49.3975   $49.40   $49.40   $49.40  
  Purchase #5 $23.67   5.175%   $24.8949   $24.89   $24.90   $24.90  
  Purchase #6 $71.73   10.392%   $79.1842   $79.18   $79.20   $79.20  
  Purchase #7 $146.33   5.796%   $154.8113   $154.81   $154.80   $154.80  
  7 purchase totals = $875.60       $945.9293   $945.91   $945.95   $946.00