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	$81.44	10.514%	$90.0026	$90.00	$90.00	$90.00
Purchase #2	$54.62	10.851%	$60.5468	$60.55	$60.55	$60.50
Purchase #3	$87.29	9.867%	$95.9029	$95.90	$95.90	$95.90
Purchase #4	$63.43	10.684%	$70.2069	$70.21	$70.20	$70.20
Purchase #5	$86.72	11.423%	$96.626	$96.63	$96.65	$96.60
Purchase #6	$241.35	7.257%	$258.8648	$258.86	$258.85	$258.90
Purchase #7	$240.27	11.735%	$268.4657	$268.47	$268.45	$268.50
7 purchase totals =	$855.12		$940.6157	$940.62	$940.60	$940.60