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 $126.75   10.130%   $139.5898   $139.59   $139.60   $139.60  
  Purchase #2 $191.95   7.237%   $205.8414   $205.84   $205.85   $205.80  
  Purchase #3 $51.87   5.651%   $54.8012   $54.80   $54.80   $54.80  
  Purchase #4 $203.40   3.702%   $210.9299   $210.93   $210.95   $210.90  
  Purchase #5 $191.38   7.288%   $205.3278   $205.33   $205.35   $205.30  
  Purchase #6 $182.43   7.132%   $195.4409   $195.44   $195.45   $195.40  
  Purchase #7 $174.36   12.356%   $195.9039   $195.90   $195.90   $195.90  
  7 purchase totals = $1,122.14       $1,207.8349   $1,207.83   $1,207.90   $1,207.70