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 $201.64   6.384%   $214.5127   $214.51   $214.50   $214.50  
  Purchase #2 $29.84   8.545%   $32.3898   $32.39   $32.40   $32.40  
  Purchase #3 $176.36   12.776%   $198.8918   $198.89   $198.90   $198.90  
  Purchase #4 $113.32   3.501%   $117.2873   $117.29   $117.30   $117.30  
  Purchase #5 $130.99   5.573%   $138.2901   $138.29   $138.30   $138.30  
  Purchase #6 $173.88   6.496%   $185.1752   $185.18   $185.20   $185.20  
  Purchase #7 $34.38   5.869%   $36.3978   $36.40   $36.40   $36.40  
  7 purchase totals = $860.41       $922.9447   $922.95   $923.00   $923.00