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 $59.70   8.714%   $64.9023   $64.90   $64.90   $64.90  
  Purchase #2 $250.54   6.701%   $267.3287   $267.33   $267.35   $267.30  
  Purchase #3 $115.79   8.701%   $125.8649   $125.86   $125.85   $125.90  
  Purchase #4 $79.78   8.269%   $86.377   $86.38   $86.40   $86.40  
  Purchase #5 $103.34   10.530%   $114.2217   $114.22   $114.20   $114.20  
  Purchase #6 $64.33   5.769%   $68.0412   $68.04   $68.05   $68.00  
  Purchase #7 $127.91   5.420%   $134.8427   $134.84   $134.85   $134.80  
  7 purchase totals = $801.39       $861.5785   $861.57   $861.60   $861.50