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 $87.71   11.474%   $97.7738   $97.77   $97.75   $97.80  
  Purchase #2 $67.95   12.244%   $76.2698   $76.27   $76.25   $76.30  
  Purchase #3 $222.86   7.420%   $239.3962   $239.40   $239.40   $239.40  
  Purchase #4 $53.72   9.592%   $58.8728   $58.87   $58.85   $58.90  
  Purchase #5 $73.73   8.767%   $80.1939   $80.19   $80.20   $80.20  
  Purchase #6 $250.93   12.587%   $282.5146   $282.51   $282.50   $282.50  
  Purchase #7 $84.37   8.202%   $91.29   $91.29   $91.30   $91.30  
  7 purchase totals = $841.27       $926.3111   $926.30   $926.25   $926.40