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	$233.44	10.872%	$258.8196	$258.82	$258.80	$258.80
Purchase #2	$109.56	12.184%	$122.9088	$122.91	$122.90	$122.90
Purchase #3	$26.87	3.567%	$27.8285	$27.83	$27.85	$27.80
Purchase #4	$22.50	7.326%	$24.1484	$24.15	$24.15	$24.10
Purchase #5	$50.67	13.228%	$57.3726	$57.37	$57.35	$57.40
Purchase #6	$53.43	11.178%	$59.4024	$59.40	$59.40	$59.40
Purchase #7	$218.39	5.774%	$230.9998	$231.00	$231.00	$231.00
7 purchase totals =	$714.86		$781.4801	$781.48	$781.45	$781.40