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	$45.35	4.173%	$47.2425	$47.24	$47.25	$47.20
Purchase #2	$39.70	7.255%	$42.5802	$42.58	$42.60	$42.60
Purchase #3	$98.36	6.562%	$104.8144	$104.81	$104.80	$104.80
Purchase #4	$165.31	10.318%	$182.3667	$182.37	$182.35	$182.40
Purchase #5	$153.90	5.623%	$162.5538	$162.55	$162.55	$162.60
Purchase #6	$202.78	13.151%	$229.4476	$229.45	$229.45	$229.40
Purchase #7	$84.30	7.536%	$90.6528	$90.65	$90.65	$90.70
7 purchase totals =	$789.70		$859.6580	$859.65	$859.65	$859.70