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	$39.31	7.455%	$42.2406	$42.24	$42.25	$42.20
Purchase #2	$49.78	12.242%	$55.8741	$55.87	$55.85	$55.90
Purchase #3	$53.44	11.318%	$59.4883	$59.49	$59.50	$59.50
Purchase #4	$149.82	13.392%	$169.8839	$169.88	$169.90	$169.90
Purchase #5	$92.28	10.134%	$101.6317	$101.63	$101.65	$101.60
Purchase #6	$170.62	13.767%	$194.1093	$194.11	$194.10	$194.10
Purchase #7	$240.45	4.255%	$250.6811	$250.68	$250.70	$250.70
7 purchase totals =	$795.70		$873.9090	$873.90	$873.95	$873.90