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	$50.58	10.420%	$55.8504	$55.85	$55.85	$55.90
Purchase #2	$71.67	12.331%	$80.5076	$80.51	$80.50	$80.50
Purchase #3	$110.33	12.451%	$124.0672	$124.07	$124.05	$124.10
Purchase #4	$112.58	9.326%	$123.0792	$123.08	$123.10	$123.10
Purchase #5	$193.29	13.539%	$219.4595	$219.46	$219.45	$219.50
Purchase #6	$60.84	5.444%	$64.1521	$64.15	$64.15	$64.20
Purchase #7	$85.60	11.354%	$95.319	$95.32	$95.30	$95.30
7 purchase totals =	$684.89		$762.4350	$762.44	$762.40	$762.60