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	$38.48	8.436%	$41.7262	$41.73	$41.75	$41.70
Purchase #2	$41.74	10.798%	$46.2471	$46.25	$46.25	$46.20
Purchase #3	$50.75	5.511%	$53.5468	$53.55	$53.55	$53.50
Purchase #4	$116.55	9.732%	$127.8926	$127.89	$127.90	$127.90
Purchase #5	$46.94	3.568%	$48.6148	$48.61	$48.60	$48.60
Purchase #6	$191.71	4.810%	$200.9313	$200.93	$200.95	$200.90
Purchase #7	$21.57	8.873%	$23.4839	$23.48	$23.50	$23.50
7 purchase totals =	$507.74		$542.4427	$542.44	$542.50	$542.30