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	$227.48	12.558%	$256.0469	$256.05	$256.05	$256.00
Purchase #2	$211.73	10.204%	$233.3349	$233.33	$233.35	$233.30
Purchase #3	$212.56	7.245%	$227.96	$227.96	$227.95	$228.00
Purchase #4	$173.68	13.396%	$196.9462	$196.95	$196.95	$196.90
Purchase #5	$106.31	4.475%	$111.0674	$111.07	$111.05	$111.10
Purchase #6	$135.73	13.481%	$154.0278	$154.03	$154.05	$154.00
Purchase #7	$244.63	11.797%	$273.489	$273.49	$273.50	$273.50
7 purchase totals =	$1,312.12		$1,452.8722	$1,452.88	$1,452.90	$1,452.80