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 $20.76   5.834%   $21.9711   $21.97   $21.95   $22.00  
  Purchase #2 $79.95   10.298%   $88.1833   $88.18   $88.20   $88.20  
  Purchase #3 $222.35   13.160%   $251.6113   $251.61   $251.60   $251.60  
  Purchase #4 $91.29   13.752%   $103.8442   $103.84   $103.85   $103.80  
  Purchase #5 $17.88   11.338%   $19.9072   $19.91   $19.90   $19.90  
  Purchase #6 $116.44   12.752%   $131.2884   $131.29   $131.30   $131.30  
  Purchase #7 $5.35   4.530%   $5.5924   $5.59   $5.60   $5.60  
  7 purchase totals = $554.02       $622.3979   $622.39   $622.40   $622.40