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	$243.32	4.137%	$253.3861	$253.39	$253.40	$253.40
Purchase #2	$120.87	13.804%	$137.5549	$137.55	$137.55	$137.60
Purchase #3	$37.88	3.567%	$39.2312	$39.23	$39.25	$39.20
Purchase #4	$41.49	11.266%	$46.1643	$46.16	$46.15	$46.20
Purchase #5	$46.63	12.663%	$52.5348	$52.53	$52.55	$52.50
Purchase #6	$131.92	9.469%	$144.4115	$144.41	$144.40	$144.40
Purchase #7	$64.64	10.518%	$71.4388	$71.44	$71.45	$71.40
7 purchase totals =	$686.75		$744.7216	$744.71	$744.75	$744.70