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 $249.70   10.498%   $275.9135   $275.91   $275.90   $275.90  
  Purchase #2 $11.86   5.154%   $12.4713   $12.47   $12.45   $12.50  
  Purchase #3 $233.98   13.657%   $265.9346   $265.93   $265.95   $265.90  
  Purchase #4 $157.33   9.407%   $172.13   $172.13   $172.15   $172.10  
  Purchase #5 $72.48   4.358%   $75.6387   $75.64   $75.65   $75.60  
  Purchase #6 $203.46   13.255%   $230.4286   $230.43   $230.45   $230.40  
  Purchase #7 $16.33   3.554%   $16.9104   $16.91   $16.90   $16.90  
  7 purchase totals = $945.14       $1,049.4271   $1,049.42   $1,049.45   $1,049.30