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	$26.34	13.322%	$29.849	$29.85	$29.85	$29.80
Purchase #2	$214.59	5.795%	$227.0255	$227.03	$227.05	$227.00
Purchase #3	$52.96	8.546%	$57.486	$57.49	$57.50	$57.50
Purchase #4	$233.54	4.373%	$243.7527	$243.75	$243.75	$243.80
Purchase #5	$137.64	6.644%	$146.7848	$146.78	$146.80	$146.80
Purchase #6	$220.76	5.673%	$233.2837	$233.28	$233.30	$233.30
Purchase #7	$180.37	4.857%	$189.1306	$189.13	$189.15	$189.10
7 purchase totals =	$1,066.20		$1,127.3123	$1,127.31	$1,127.40	$1,127.30