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 $154.74   12.863%   $174.6442   $174.64   $174.65   $174.60  
  Purchase #2 $130.98   9.645%   $143.613   $143.61   $143.60   $143.60  
  Purchase #3 $144.59   13.686%   $164.3786   $164.38   $164.40   $164.40  
  Purchase #4 $52.72   6.728%   $56.267   $56.27   $56.25   $56.30  
  Purchase #5 $118.99   5.287%   $125.281   $125.28   $125.30   $125.30  
  Purchase #6 $44.95   8.567%   $48.8009   $48.80   $48.80   $48.80  
  Purchase #7 $197.76   8.143%   $213.8636   $213.86   $213.85   $213.90  
  7 purchase totals = $844.73       $926.8483   $926.84   $926.85   $926.90