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	$79.33	12.194%	$89.0035	$89.00	$89.00	$89.00
Purchase #2	$9.83	7.147%	$10.5326	$10.53	$10.55	$10.50
Purchase #3	$132.46	8.518%	$143.7429	$143.74	$143.75	$143.70
Purchase #4	$242.86	3.533%	$251.4402	$251.44	$251.45	$251.40
Purchase #5	$154.67	8.462%	$167.7582	$167.76	$167.75	$167.80
Purchase #6	$82.47	8.754%	$89.6894	$89.69	$89.70	$89.70
Purchase #7	$84.66	9.230%	$92.4741	$92.47	$92.45	$92.50
7 purchase totals =	$786.28		$844.6409	$844.63	$844.65	$844.60