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	$54.52	5.855%	$57.7121	$57.71	$57.70	$57.70
Purchase #2	$72.50	7.852%	$78.1927	$78.19	$78.20	$78.20
Purchase #3	$188.68	3.691%	$195.6442	$195.64	$195.65	$195.60
Purchase #4	$155.35	12.272%	$174.4146	$174.41	$174.40	$174.40
Purchase #5	$11.91	3.621%	$12.3413	$12.34	$12.35	$12.30
Purchase #6	$240.39	12.269%	$269.8834	$269.88	$269.90	$269.90
Purchase #7	$115.52	6.729%	$123.2933	$123.29	$123.30	$123.30
7 purchase totals =	$838.87		$911.4816	$911.46	$911.50	$911.40