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	$226.56	9.675%	$248.4797	$248.48	$248.50	$248.50
Purchase #2	$62.64	12.213%	$70.2902	$70.29	$70.30	$70.30
Purchase #3	$24.92	13.571%	$28.3019	$28.30	$28.30	$28.30
Purchase #4	$236.34	3.479%	$244.5623	$244.56	$244.55	$244.60
Purchase #5	$218.47	9.120%	$238.3945	$238.39	$238.40	$238.40
Purchase #6	$86.54	3.361%	$89.4486	$89.45	$89.45	$89.40
Purchase #7	$114.27	6.708%	$121.9352	$121.94	$121.95	$121.90
7 purchase totals =	$969.74		$1,041.4124	$1,041.41	$1,041.45	$1,041.40