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	$59.85	11.334%	$66.6334	$66.63	$66.65	$66.60
Purchase #2	$220.78	9.643%	$242.0698	$242.07	$242.05	$242.10
Purchase #3	$236.52	3.332%	$244.4008	$244.40	$244.40	$244.40
Purchase #4	$97.79	7.242%	$104.872	$104.87	$104.85	$104.90
Purchase #5	$33.56	5.129%	$35.2813	$35.28	$35.30	$35.30
Purchase #6	$194.37	10.774%	$215.3114	$215.31	$215.30	$215.30
Purchase #7	$65.43	6.318%	$69.5639	$69.56	$69.55	$69.60
7 purchase totals =	$908.30		$978.1326	$978.12	$978.10	$978.20