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 $41.46   8.117%   $44.8253   $44.83   $44.85   $44.80  
  Purchase #2 $140.63   9.484%   $153.9673   $153.97   $153.95   $154.00  
  Purchase #3 $210.72   10.607%   $233.0711   $233.07   $233.05   $233.10  
  Purchase #4 $143.26   12.623%   $161.3437   $161.34   $161.35   $161.30  
  Purchase #5 $167.70   7.651%   $180.5307   $180.53   $180.55   $180.50  
  Purchase #6 $155.72   13.237%   $176.3327   $176.33   $176.35   $176.30  
  Purchase #7 $96.92   8.496%   $105.1543   $105.15   $105.15   $105.20  
  7 purchase totals = $956.41       $1,055.2251   $1,055.22   $1,055.25   $1,055.20