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	$80.76	10.837%	$89.512	$89.51	$89.50	$89.50
Purchase #2	$101.74	7.245%	$109.1111	$109.11	$109.10	$109.10
Purchase #3	$179.80	7.390%	$193.0872	$193.09	$193.10	$193.10
Purchase #4	$173.83	3.477%	$179.8741	$179.87	$179.85	$179.90
Purchase #5	$50.67	13.463%	$57.4917	$57.49	$57.50	$57.50
Purchase #6	$47.66	9.749%	$52.3064	$52.31	$52.30	$52.30
Purchase #7	$47.46	9.789%	$52.1059	$52.11	$52.10	$52.10
7 purchase totals =	$681.92		$733.4884	$733.49	$733.45	$733.50