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	$240.89	4.294%	$251.2338	$251.23	$251.25	$251.20
Purchase #2	$56.72	10.142%	$62.4725	$62.47	$62.45	$62.50
Purchase #3	$56.76	4.791%	$59.4794	$59.48	$59.50	$59.50
Purchase #4	$247.42	6.831%	$264.3213	$264.32	$264.30	$264.30
Purchase #5	$181.43	9.539%	$198.7366	$198.74	$198.75	$198.70
Purchase #6	$78.74	13.306%	$89.2171	$89.22	$89.20	$89.20
Purchase #7	$221.72	3.324%	$229.09	$229.09	$229.10	$229.10
7 purchase totals =	$1,083.68		$1,154.5507	$1,154.55	$1,154.55	$1,154.50