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	$117.39	11.873%	$131.3277	$131.33	$131.35	$131.30
Purchase #2	$248.33	4.361%	$259.1597	$259.16	$259.15	$259.20
Purchase #3	$57.67	5.794%	$61.0114	$61.01	$61.00	$61.00
Purchase #4	$132.31	10.511%	$146.2171	$146.22	$146.20	$146.20
Purchase #5	$196.62	10.152%	$216.5809	$216.58	$216.60	$216.60
Purchase #6	$92.42	5.133%	$97.1639	$97.16	$97.15	$97.20
Purchase #7	$149.55	13.440%	$169.6495	$169.65	$169.65	$169.60
7 purchase totals =	$994.29		$1,081.1102	$1,081.11	$1,081.10	$1,081.10