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	$72.52	8.152%	$78.4318	$78.43	$78.45	$78.40
Purchase #2	$114.43	11.253%	$127.3068	$127.31	$127.30	$127.30
Purchase #3	$237.45	12.215%	$266.4545	$266.45	$266.45	$266.50
Purchase #4	$150.37	11.376%	$167.4761	$167.48	$167.50	$167.50
Purchase #5	$130.91	6.494%	$139.4113	$139.41	$139.40	$139.40
Purchase #6	$176.94	6.123%	$187.774	$187.77	$187.75	$187.80
Purchase #7	$17.58	3.272%	$18.1552	$18.16	$18.15	$18.20
7 purchase totals =	$900.20		$985.0097	$985.01	$985.00	$985.10