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	$53.39	12.181%	$59.8934	$59.89	$59.90	$59.90
Purchase #2	$85.85	7.502%	$92.2905	$92.29	$92.30	$92.30
Purchase #3	$149.28	6.294%	$158.6757	$158.68	$158.70	$158.70
Purchase #4	$145.80	10.339%	$160.8743	$160.87	$160.85	$160.90
Purchase #5	$51.33	7.835%	$55.3517	$55.35	$55.35	$55.40
Purchase #6	$17.89	9.838%	$19.65	$19.65	$19.65	$19.70
Purchase #7	$222.44	13.228%	$251.8644	$251.86	$251.85	$251.90
7 purchase totals =	$725.98		$798.6000	$798.59	$798.60	$798.80