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	$37.64	11.600%	$42.0062	$42.01	$42.00	$42.00
Purchase #2	$52.36	3.261%	$54.0675	$54.07	$54.05	$54.10
Purchase #3	$67.83	7.848%	$73.1533	$73.15	$73.15	$73.20
Purchase #4	$166.27	6.321%	$176.7799	$176.78	$176.80	$176.80
Purchase #5	$155.47	7.708%	$167.4536	$167.45	$167.45	$167.50
Purchase #6	$129.93	5.706%	$137.3438	$137.34	$137.35	$137.30
Purchase #7	$229.71	4.504%	$240.0561	$240.06	$240.05	$240.10
7 purchase totals =	$839.21		$890.8604	$890.86	$890.85	$891.00