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	$228.89	9.381%	$250.3622	$250.36	$250.35	$250.40
Purchase #2	$9.90	11.258%	$11.0145	$11.01	$11.00	$11.00
Purchase #3	$100.25	12.810%	$113.092	$113.09	$113.10	$113.10
Purchase #4	$141.88	10.251%	$156.4241	$156.42	$156.40	$156.40
Purchase #5	$65.44	7.792%	$70.5391	$70.54	$70.55	$70.50
Purchase #6	$49.89	6.554%	$53.1598	$53.16	$53.15	$53.20
Purchase #7	$236.60	5.797%	$250.3157	$250.32	$250.30	$250.30
7 purchase totals =	$832.85		$904.9074	$904.90	$904.85	$904.90