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	$100.91	3.724%	$104.6679	$104.67	$104.65	$104.70
Purchase #2	$178.30	6.218%	$189.3867	$189.39	$189.40	$189.40
Purchase #3	$195.41	13.696%	$222.1734	$222.17	$222.15	$222.20
Purchase #4	$21.31	3.871%	$22.1349	$22.13	$22.15	$22.10
Purchase #5	$229.83	3.755%	$238.4601	$238.46	$238.45	$238.50
Purchase #6	$7.30	8.310%	$7.9066	$7.91	$7.90	$7.90
Purchase #7	$82.72	8.343%	$89.6213	$89.62	$89.60	$89.60
7 purchase totals =	$815.78		$874.3509	$874.35	$874.30	$874.40