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	$125.89	4.414%	$131.4468	$131.45	$131.45	$131.40
Purchase #2	$181.94	7.630%	$195.822	$195.82	$195.80	$195.80
Purchase #3	$108.42	5.371%	$114.2432	$114.24	$114.25	$114.20
Purchase #4	$52.26	13.637%	$59.3867	$59.39	$59.40	$59.40
Purchase #5	$127.49	13.568%	$144.7878	$144.79	$144.80	$144.80
Purchase #6	$53.79	10.482%	$59.4283	$59.43	$59.45	$59.40
Purchase #7	$212.77	10.108%	$234.2768	$234.28	$234.30	$234.30
7 purchase totals =	$862.56		$939.3916	$939.40	$939.45	$939.30