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 $69.59   12.822%   $78.5128   $78.51   $78.50   $78.50  
  Purchase #2 $91.33   12.677%   $102.9079   $102.91   $102.90   $102.90  
  Purchase #3 $194.81   3.631%   $201.8836   $201.88   $201.90   $201.90  
  Purchase #4 $94.84   13.402%   $107.5505   $107.55   $107.55   $107.60  
  Purchase #5 $9.84   13.247%   $11.1435   $11.14   $11.15   $11.10  
  Purchase #6 $185.36   11.580%   $206.8247   $206.82   $206.80   $206.80  
  Purchase #7 $109.58   13.834%   $124.7393   $124.74   $124.75   $124.70  
  7 purchase totals = $755.35       $833.5623   $833.55   $833.55   $833.50