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	$30.55	3.330%	$31.5673	$31.57	$31.55	$31.60
Purchase #2	$214.79	5.391%	$226.3693	$226.37	$226.35	$226.40
Purchase #3	$225.26	9.595%	$246.8737	$246.87	$246.85	$246.90
Purchase #4	$41.89	7.287%	$44.9425	$44.94	$44.95	$44.90
Purchase #5	$250.48	9.169%	$273.4465	$273.45	$273.45	$273.40
Purchase #6	$245.45	8.141%	$265.4321	$265.43	$265.45	$265.40
Purchase #7	$200.90	5.482%	$211.9133	$211.91	$211.90	$211.90
7 purchase totals =	$1,209.32		$1,300.5447	$1,300.54	$1,300.50	$1,300.50