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 $183.87   11.523%   $205.0573   $205.06   $205.05   $205.10  
  Purchase #2 $71.29   11.799%   $79.7015   $79.70   $79.70   $79.70  
  Purchase #3 $249.66   13.230%   $282.69   $282.69   $282.70   $282.70  
  Purchase #4 $50.62   10.388%   $55.8784   $55.88   $55.90   $55.90  
  Purchase #5 $179.51   5.453%   $189.2987   $189.30   $189.30   $189.30  
  Purchase #6 $94.98   3.424%   $98.2321   $98.23   $98.25   $98.20  
  Purchase #7 $125.62   5.648%   $132.715   $132.72   $132.70   $132.70  
  7 purchase totals = $955.55       $1,043.5730   $1,043.58   $1,043.60   $1,043.60