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 $104.41   13.332%   $118.3299   $118.33   $118.35   $118.30  
  Purchase #2 $98.51   5.282%   $103.7133   $103.71   $103.70   $103.70  
  Purchase #3 $93.28   5.243%   $98.1707   $98.17   $98.15   $98.20  
  Purchase #4 $56.83   7.572%   $61.1332   $61.13   $61.15   $61.10  
  Purchase #5 $87.47   9.109%   $95.4376   $95.44   $95.45   $95.40  
  Purchase #6 $214.97   13.639%   $244.2898   $244.29   $244.30   $244.30  
  Purchase #7 $161.36   13.598%   $183.3017   $183.30   $183.30   $183.30  
  7 purchase totals = $816.83       $904.3762   $904.37   $904.40   $904.30