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	$189.31	10.850%	$209.8501	$209.85	$209.85	$209.90
Purchase #2	$48.26	3.860%	$50.1228	$50.12	$50.10	$50.10
Purchase #3	$93.77	13.584%	$106.5077	$106.51	$106.50	$106.50
Purchase #4	$165.78	8.634%	$180.0934	$180.09	$180.10	$180.10
Purchase #5	$187.60	4.714%	$196.4435	$196.44	$196.45	$196.40
Purchase #6	$155.99	11.265%	$173.5623	$173.56	$173.55	$173.60
Purchase #7	$215.85	10.790%	$239.1402	$239.14	$239.15	$239.10
7 purchase totals =	$1,056.56		$1,155.7200	$1,155.71	$1,155.70	$1,155.70