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	$229.58	4.725%	$240.4277	$240.43	$240.45	$240.40
Purchase #2	$40.70	6.625%	$43.3964	$43.40	$43.40	$43.40
Purchase #3	$147.55	7.465%	$158.5646	$158.56	$158.55	$158.60
Purchase #4	$127.85	13.379%	$144.9551	$144.96	$144.95	$145.00
Purchase #5	$86.73	3.670%	$89.913	$89.91	$89.90	$89.90
Purchase #6	$126.94	12.468%	$142.7669	$142.77	$142.75	$142.80
Purchase #7	$60.68	11.652%	$67.7504	$67.75	$67.75	$67.80
7 purchase totals =	$820.03		$887.7741	$887.78	$887.75	$887.90