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 $233.28   10.618%   $258.0497   $258.05   $258.05   $258.00  
  Purchase #2 $176.48   13.138%   $199.6659   $199.67   $199.65   $199.70  
  Purchase #3 $195.38   13.278%   $221.3226   $221.32   $221.30   $221.30  
  Purchase #4 $81.56   5.116%   $85.7326   $85.73   $85.75   $85.70  
  Purchase #5 $16.58   13.181%   $18.7654   $18.77   $18.75   $18.80  
  Purchase #6 $161.84   6.743%   $172.7529   $172.75   $172.75   $172.80  
  Purchase #7 $198.47   5.623%   $209.63   $209.63   $209.65   $209.60  
  7 purchase totals = $1,063.59       $1,165.9191   $1,165.92   $1,165.90   $1,165.90