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 $194.74   6.144%   $206.7048   $206.70   $206.70   $206.70  
  Purchase #2 $154.73   8.851%   $168.4252   $168.43   $168.45   $168.40  
  Purchase #3 $103.67   5.463%   $109.3335   $109.33   $109.35   $109.30  
  Purchase #4 $238.93   8.440%   $259.0957   $259.10   $259.10   $259.10  
  Purchase #5 $205.90   12.844%   $232.3458   $232.35   $232.35   $232.30  
  Purchase #6 $180.85   7.491%   $194.3975   $194.40   $194.40   $194.40  
  Purchase #7 $76.86   11.847%   $85.9656   $85.97   $85.95   $86.00  
  7 purchase totals = $1,155.68       $1,256.2681   $1,256.28   $1,256.30   $1,256.20