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	$249.77	3.362%	$258.1673	$258.17	$258.15	$258.20
Purchase #2	$83.85	5.826%	$88.7351	$88.74	$88.75	$88.70
Purchase #3	$95.44	7.347%	$102.452	$102.45	$102.45	$102.50
Purchase #4	$240.87	5.745%	$254.708	$254.71	$254.70	$254.70
Purchase #5	$61.91	4.229%	$64.5282	$64.53	$64.55	$64.50
Purchase #6	$81.43	12.664%	$91.7423	$91.74	$91.75	$91.70
Purchase #7	$108.29	13.835%	$123.2719	$123.27	$123.25	$123.30
7 purchase totals =	$921.56		$983.6048	$983.61	$983.60	$983.60