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	$140.63	13.471%	$159.5743	$159.57	$159.55	$159.60
Purchase #2	$225.78	4.449%	$235.825	$235.83	$235.85	$235.80
Purchase #3	$15.98	10.164%	$17.6042	$17.60	$17.60	$17.60
Purchase #4	$110.56	3.392%	$114.3102	$114.31	$114.30	$114.30
Purchase #5	$110.56	11.269%	$123.019	$123.02	$123.00	$123.00
Purchase #6	$166.43	4.221%	$173.455	$173.46	$173.45	$173.50
Purchase #7	$14.77	4.840%	$15.4849	$15.48	$15.50	$15.50
7 purchase totals =	$784.71		$839.2726	$839.27	$839.25	$839.30