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	$19.73	5.587%	$20.8323	$20.83	$20.85	$20.80
Purchase #2	$157.79	4.755%	$165.2929	$165.29	$165.30	$165.30
Purchase #3	$145.74	3.844%	$151.3422	$151.34	$151.35	$151.30
Purchase #4	$154.25	11.148%	$171.4458	$171.45	$171.45	$171.40
Purchase #5	$43.37	4.182%	$45.1837	$45.18	$45.20	$45.20
Purchase #6	$51.39	5.536%	$54.235	$54.24	$54.25	$54.20
Purchase #7	$98.76	3.500%	$102.2166	$102.22	$102.20	$102.20
7 purchase totals =	$671.03		$710.5485	$710.55	$710.60	$710.40