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	$35.32	13.345%	$40.0335	$40.03	$40.05	$40.00
Purchase #2	$12.80	12.111%	$14.3502	$14.35	$14.35	$14.40
Purchase #3	$184.91	12.842%	$208.6561	$208.66	$208.65	$208.70
Purchase #4	$128.97	8.343%	$139.73	$139.73	$139.75	$139.70
Purchase #5	$86.53	3.698%	$89.7299	$89.73	$89.75	$89.70
Purchase #6	$248.50	12.123%	$278.6257	$278.63	$278.65	$278.60
Purchase #7	$249.45	12.174%	$279.818	$279.82	$279.80	$279.80
7 purchase totals =	$946.48		$1,050.9434	$1,050.95	$1,051.00	$1,050.90