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 $69.53   5.698%   $73.4918   $73.49   $73.50   $73.50  
  Purchase #2 $197.41   9.170%   $215.5125   $215.51   $215.50   $215.50  
  Purchase #3 $6.73   3.276%   $6.9505   $6.95   $6.95   $7.00  
  Purchase #4 $60.82   8.669%   $66.0925   $66.09   $66.10   $66.10  
  Purchase #5 $130.67   8.754%   $142.1089   $142.11   $142.10   $142.10  
  Purchase #6 $87.32   7.821%   $94.1493   $94.15   $94.15   $94.10  
  Purchase #7 $72.70   4.535%   $75.9969   $76.00   $76.00   $76.00  
  7 purchase totals = $625.18       $674.3024   $674.30   $674.30   $674.30