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	$99.91	8.429%	$108.3314	$108.33	$108.35	$108.30
Purchase #2	$147.46	13.429%	$167.2624	$167.26	$167.25	$167.30
Purchase #3	$88.68	13.496%	$100.6483	$100.65	$100.65	$100.60
Purchase #4	$5.39	3.806%	$5.5951	$5.60	$5.60	$5.60
Purchase #5	$44.78	7.808%	$48.2764	$48.28	$48.30	$48.30
Purchase #6	$86.34	5.604%	$91.1785	$91.18	$91.20	$91.20
Purchase #7	$223.57	12.668%	$251.8918	$251.89	$251.90	$251.90
7 purchase totals =	$696.13		$773.1839	$773.19	$773.25	$773.20