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	$226.82	11.451%	$252.7932	$252.79	$252.80	$252.80
Purchase #2	$20.29	3.837%	$21.0685	$21.07	$21.05	$21.10
Purchase #3	$99.90	13.447%	$113.3336	$113.33	$113.35	$113.30
Purchase #4	$109.93	6.849%	$117.4591	$117.46	$117.45	$117.50
Purchase #5	$146.32	6.765%	$156.2185	$156.22	$156.20	$156.20
Purchase #6	$167.50	3.578%	$173.4932	$173.49	$173.50	$173.50
Purchase #7	$244.54	10.715%	$270.7425	$270.74	$270.75	$270.70
7 purchase totals =	$1,015.30		$1,105.1086	$1,105.10	$1,105.10	$1,105.10