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	$27.39	4.531%	$28.631	$28.63	$28.65	$28.60
Purchase #2	$55.84	4.571%	$58.3924	$58.39	$58.40	$58.40
Purchase #3	$11.59	5.414%	$12.2175	$12.22	$12.20	$12.20
Purchase #4	$231.45	11.658%	$258.4324	$258.43	$258.45	$258.40
Purchase #5	$206.41	12.538%	$232.2897	$232.29	$232.30	$232.30
Purchase #6	$120.41	6.197%	$127.8718	$127.87	$127.85	$127.90
Purchase #7	$39.41	6.574%	$42.0008	$42.00	$42.00	$42.00
7 purchase totals =	$692.50		$759.8356	$759.83	$759.85	$759.80