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 $184.26   11.784%   $205.9732   $205.97   $205.95   $206.00  
  Purchase #2 $205.61   11.711%   $229.689   $229.69   $229.70   $229.70  
  Purchase #3 $132.77   10.119%   $146.205   $146.21   $146.20   $146.20  
  Purchase #4 $157.61   6.172%   $167.3377   $167.34   $167.35   $167.30  
  Purchase #5 $240.67   4.176%   $250.7204   $250.72   $250.70   $250.70  
  Purchase #6 $219.31   6.679%   $233.9577   $233.96   $233.95   $234.00  
  Purchase #7 $151.71   3.707%   $157.3339   $157.33   $157.35   $157.30  
  7 purchase totals = $1,291.94       $1,391.2169   $1,391.22   $1,391.20   $1,391.20