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	$126.90	13.686%	$144.2675	$144.27	$144.25	$144.30
Purchase #2	$161.51	4.491%	$168.7634	$168.76	$168.75	$168.80
Purchase #3	$238.58	7.666%	$256.8695	$256.87	$256.85	$256.90
Purchase #4	$31.86	10.802%	$35.3015	$35.30	$35.30	$35.30
Purchase #5	$48.29	10.323%	$53.275	$53.28	$53.30	$53.30
Purchase #6	$29.41	6.407%	$31.2943	$31.29	$31.30	$31.30
Purchase #7	$42.71	9.627%	$46.8217	$46.82	$46.80	$46.80
7 purchase totals =	$679.26		$736.5929	$736.59	$736.55	$736.70