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	$83.98	8.156%	$90.8294	$90.83	$90.85	$90.80
Purchase #2	$37.59	12.600%	$42.3263	$42.33	$42.35	$42.30
Purchase #3	$28.72	8.508%	$31.1635	$31.16	$31.15	$31.20
Purchase #4	$148.81	6.488%	$158.4648	$158.46	$158.45	$158.50
Purchase #5	$84.52	11.729%	$94.4334	$94.43	$94.45	$94.40
Purchase #6	$33.35	9.722%	$36.5923	$36.59	$36.60	$36.60
Purchase #7	$145.31	9.263%	$158.7701	$158.77	$158.75	$158.80
7 purchase totals =	$562.28		$612.5798	$612.57	$612.60	$612.60