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	$93.51	7.379%	$100.4101	$100.41	$100.40	$100.40
Purchase #2	$155.74	6.760%	$166.268	$166.27	$166.25	$166.30
Purchase #3	$159.85	10.163%	$176.0956	$176.10	$176.10	$176.10
Purchase #4	$155.46	6.574%	$165.6799	$165.68	$165.70	$165.70
Purchase #5	$138.63	4.228%	$144.4913	$144.49	$144.50	$144.50
Purchase #6	$93.91	6.302%	$99.8282	$99.83	$99.85	$99.80
Purchase #7	$169.73	10.703%	$187.8962	$187.90	$187.90	$187.90
7 purchase totals =	$966.83		$1,040.6693	$1,040.68	$1,040.70	$1,040.70