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 $224.66   4.736%   $235.2999   $235.30   $235.30   $235.30  
  Purchase #2 $63.40   6.677%   $67.6332   $67.63   $67.65   $67.60  
  Purchase #3 $194.65   3.197%   $200.873   $200.87   $200.85   $200.90  
  Purchase #4 $246.66   3.728%   $255.8555   $255.86   $255.85   $255.90  
  Purchase #5 $159.40   9.795%   $175.0132   $175.01   $175.00   $175.00  
  Purchase #6 $170.79   4.530%   $178.5268   $178.53   $178.55   $178.50  
  Purchase #7 $227.53   11.109%   $252.8063   $252.81   $252.80   $252.80  
  7 purchase totals = $1,287.09       $1,366.0079   $1,366.01   $1,366.00   $1,366.00