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	$54.39	9.370%	$59.4863	$59.49	$59.50	$59.50
Purchase #2	$238.43	5.551%	$251.6652	$251.67	$251.65	$251.70
Purchase #3	$48.30	13.710%	$54.9219	$54.92	$54.90	$54.90
Purchase #4	$174.42	6.281%	$185.3753	$185.38	$185.40	$185.40
Purchase #5	$20.28	11.137%	$22.5386	$22.54	$22.55	$22.50
Purchase #6	$123.87	13.166%	$140.1787	$140.18	$140.20	$140.20
Purchase #7	$120.80	3.192%	$124.6559	$124.66	$124.65	$124.70
7 purchase totals =	$780.49		$838.8219	$838.84	$838.85	$838.90