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 $49.93   13.682%   $56.7614   $56.76   $56.75   $56.80  
  Purchase #2 $82.92   3.425%   $85.76   $85.76   $85.75   $85.80  
  Purchase #3 $229.78   12.144%   $257.6845   $257.68   $257.70   $257.70  
  Purchase #4 $96.71   11.203%   $107.5444   $107.54   $107.55   $107.50  
  Purchase #5 $241.36   10.771%   $267.3569   $267.36   $267.35   $267.40  
  Purchase #6 $224.56   8.726%   $244.1551   $244.16   $244.15   $244.20  
  Purchase #7 $221.90   8.394%   $240.5263   $240.53   $240.55   $240.50  
  7 purchase totals = $1,147.16       $1,259.7886   $1,259.79   $1,259.80   $1,259.90