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	$79.89	12.528%	$89.8986	$89.90	$89.90	$89.90
Purchase #2	$154.52	3.194%	$159.4554	$159.46	$159.45	$159.50
Purchase #3	$54.92	3.180%	$56.6665	$56.67	$56.65	$56.70
Purchase #4	$31.83	3.199%	$32.8482	$32.85	$32.85	$32.80
Purchase #5	$247.29	9.655%	$271.1658	$271.17	$271.15	$271.20
Purchase #6	$125.53	6.292%	$133.4283	$133.43	$133.45	$133.40
Purchase #7	$210.55	7.586%	$226.5223	$226.52	$226.50	$226.50
7 purchase totals =	$904.53		$969.9851	$970.00	$969.95	$970.00