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 $208.92   5.323%   $220.0408   $220.04   $220.05   $220.00  
  Purchase #2 $33.99   9.152%   $37.1008   $37.10   $37.10   $37.10  
  Purchase #3 $136.82   5.155%   $143.8731   $143.87   $143.85   $143.90  
  Purchase #4 $85.62   12.506%   $96.3276   $96.33   $96.35   $96.30  
  Purchase #5 $11.43   7.387%   $12.2743   $12.27   $12.25   $12.30  
  Purchase #6 $120.97   4.314%   $126.1886   $126.19   $126.20   $126.20  
  Purchase #7 $168.49   8.482%   $182.7813   $182.78   $182.80   $182.80  
  7 purchase totals = $766.24       $818.5865   $818.58   $818.60   $818.60