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 $16.76   3.593%   $17.3622   $17.36   $17.35   $17.40  
  Purchase #2 $246.29   11.563%   $274.7685   $274.77   $274.75   $274.80  
  Purchase #3 $155.74   12.125%   $174.6235   $174.62   $174.60   $174.60  
  Purchase #4 $185.88   10.171%   $204.7859   $204.79   $204.80   $204.80  
  Purchase #5 $205.81   4.827%   $215.7444   $215.74   $215.75   $215.70  
  Purchase #6 $42.33   7.103%   $45.3367   $45.34   $45.35   $45.30  
  Purchase #7 $122.32   3.673%   $126.8128   $126.81   $126.80   $126.80  
  7 purchase totals = $975.13       $1,059.4340   $1,059.43   $1,059.40   $1,059.40