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	$91.48	12.499%	$102.9141	$102.91	$102.90	$102.90
Purchase #2	$160.56	3.560%	$166.2759	$166.28	$166.30	$166.30
Purchase #3	$173.41	13.531%	$196.8741	$196.87	$196.85	$196.90
Purchase #4	$17.67	7.108%	$18.926	$18.93	$18.95	$18.90
Purchase #5	$14.28	4.873%	$14.9759	$14.98	$15.00	$15.00
Purchase #6	$183.61	10.842%	$203.517	$203.52	$203.50	$203.50
Purchase #7	$88.82	12.176%	$99.6347	$99.63	$99.65	$99.60
7 purchase totals =	$729.83		$803.1177	$803.12	$803.15	$803.10