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	$173.61	6.124%	$184.2419	$184.24	$184.25	$184.20
Purchase #2	$131.34	4.544%	$137.3081	$137.31	$137.30	$137.30
Purchase #3	$101.78	9.241%	$111.1855	$111.19	$111.20	$111.20
Purchase #4	$183.44	3.638%	$190.1135	$190.11	$190.10	$190.10
Purchase #5	$181.50	13.188%	$205.4362	$205.44	$205.45	$205.40
Purchase #6	$154.65	8.197%	$167.3267	$167.33	$167.35	$167.30
Purchase #7	$86.56	5.189%	$91.0516	$91.05	$91.05	$91.10
7 purchase totals =	$1,012.88		$1,086.6635	$1,086.67	$1,086.70	$1,086.60