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 $215.53   4.874%   $226.0349   $226.03   $226.05   $226.00  
  Purchase #2 $99.87   9.394%   $109.2518   $109.25   $109.25   $109.30  
  Purchase #3 $67.48   3.559%   $69.8816   $69.88   $69.90   $69.90  
  Purchase #4 $55.91   8.219%   $60.5052   $60.51   $60.50   $60.50  
  Purchase #5 $121.78   3.309%   $125.8097   $125.81   $125.80   $125.80  
  Purchase #6 $7.46   6.321%   $7.9315   $7.93   $7.95   $7.90  
  Purchase #7 $147.58   4.610%   $154.3834   $154.38   $154.40   $154.40  
  7 purchase totals = $715.61       $753.7981   $753.79   $753.85   $753.80