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	$107.67	13.689%	$122.4089	$122.41	$122.40	$122.40
Purchase #2	$243.58	6.771%	$260.0728	$260.07	$260.05	$260.10
Purchase #3	$88.83	13.558%	$100.8736	$100.87	$100.85	$100.90
Purchase #4	$209.33	12.713%	$235.9421	$235.94	$235.95	$235.90
Purchase #5	$54.30	10.318%	$59.9027	$59.90	$59.90	$59.90
Purchase #6	$142.66	13.668%	$162.1588	$162.16	$162.15	$162.20
Purchase #7	$50.27	7.182%	$53.8804	$53.88	$53.90	$53.90
7 purchase totals =	$896.64		$995.2393	$995.23	$995.20	$995.30