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 $168.61   9.672%   $184.918   $184.92   $184.90   $184.90  
  Purchase #2 $35.47   11.783%   $39.6494   $39.65   $39.65   $39.60  
  Purchase #3 $45.44   3.295%   $46.9372   $46.94   $46.95   $46.90  
  Purchase #4 $79.39   9.473%   $86.9106   $86.91   $86.90   $86.90  
  Purchase #5 $13.41   5.555%   $14.1549   $14.15   $14.15   $14.20  
  Purchase #6 $151.41   6.769%   $161.6589   $161.66   $161.65   $161.70  
  Purchase #7 $42.42   11.552%   $47.3204   $47.32   $47.30   $47.30  
  7 purchase totals = $536.15       $581.5494   $581.55   $581.50   $581.50