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	$48.29	7.494%	$51.9089	$51.91	$51.90	$51.90
Purchase #2	$85.91	8.158%	$92.9185	$92.92	$92.90	$92.90
Purchase #3	$115.51	10.444%	$127.5739	$127.57	$127.55	$127.60
Purchase #4	$69.29	3.526%	$71.7332	$71.73	$71.75	$71.70
Purchase #5	$144.32	12.779%	$162.7627	$162.76	$162.75	$162.80
Purchase #6	$116.50	9.613%	$127.6991	$127.70	$127.70	$127.70
Purchase #7	$46.95	4.137%	$48.8923	$48.89	$48.90	$48.90
7 purchase totals =	$626.77		$683.4886	$683.48	$683.45	$683.50