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 $190.87   8.419%   $206.9393   $206.94   $206.95   $206.90  
  Purchase #2 $239.89   11.446%   $267.3478   $267.35   $267.35   $267.30  
  Purchase #3 $216.42   13.258%   $245.113   $245.11   $245.10   $245.10  
  Purchase #4 $171.26   6.678%   $182.6967   $182.70   $182.70   $182.70  
  Purchase #5 $77.72   11.622%   $86.7526   $86.75   $86.75   $86.80  
  Purchase #6 $202.39   5.262%   $213.0398   $213.04   $213.05   $213.00  
  Purchase #7 $6.84   10.259%   $7.5417   $7.54   $7.55   $7.50  
  7 purchase totals = $1,105.39       $1,209.4309   $1,209.43   $1,209.45   $1,209.30