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	$230.74	3.520%	$238.862	$238.86	$238.85	$238.90
Purchase #2	$196.78	11.338%	$219.0909	$219.09	$219.10	$219.10
Purchase #3	$84.61	5.621%	$89.3659	$89.37	$89.35	$89.40
Purchase #4	$197.69	7.847%	$213.2027	$213.20	$213.20	$213.20
Purchase #5	$223.47	12.174%	$250.6752	$250.68	$250.70	$250.70
Purchase #6	$47.30	12.263%	$53.1004	$53.10	$53.10	$53.10
Purchase #7	$21.84	12.327%	$24.5322	$24.53	$24.55	$24.50
7 purchase totals =	$1,002.43		$1,088.8293	$1,088.83	$1,088.85	$1,088.90