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	$198.28	13.532%	$225.1112	$225.11	$225.10	$225.10
Purchase #2	$211.84	11.416%	$236.0237	$236.02	$236.00	$236.00
Purchase #3	$215.27	3.271%	$222.3115	$222.31	$222.30	$222.30
Purchase #4	$231.68	6.191%	$246.0233	$246.02	$246.00	$246.00
Purchase #5	$123.33	13.276%	$139.7033	$139.70	$139.70	$139.70
Purchase #6	$50.27	4.632%	$52.5985	$52.60	$52.60	$52.60
Purchase #7	$89.77	13.433%	$101.8288	$101.83	$101.85	$101.80
7 purchase totals =	$1,120.44		$1,223.6003	$1,223.59	$1,223.55	$1,223.50