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 $199.76   5.226%   $210.1995   $210.20   $210.20   $210.20  
  Purchase #2 $239.84   9.665%   $263.0205   $263.02   $263.00   $263.00  
  Purchase #3 $19.31   7.509%   $20.76   $20.76   $20.75   $20.80  
  Purchase #4 $90.25   7.303%   $96.841   $96.84   $96.85   $96.80  
  Purchase #5 $158.46   8.782%   $172.376   $172.38   $172.40   $172.40  
  Purchase #6 $195.49   8.623%   $212.3471   $212.35   $212.35   $212.30  
  Purchase #7 $116.56   10.220%   $128.4724   $128.47   $128.45   $128.50  
  7 purchase totals = $1,019.67       $1,104.0165   $1,104.02   $1,104.00   $1,104.00