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	$150.97	9.578%	$165.4299	$165.43	$165.45	$165.40
Purchase #2	$133.66	10.551%	$147.7625	$147.76	$147.75	$147.80
Purchase #3	$74.95	5.814%	$79.3076	$79.31	$79.30	$79.30
Purchase #4	$38.36	13.409%	$43.5037	$43.50	$43.50	$43.50
Purchase #5	$153.73	11.816%	$171.8947	$171.89	$171.90	$171.90
Purchase #6	$183.74	4.125%	$191.3193	$191.32	$191.30	$191.30
Purchase #7	$103.44	7.809%	$111.5176	$111.52	$111.50	$111.50
7 purchase totals =	$838.85		$910.7353	$910.73	$910.70	$910.70