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	$70.34	4.806%	$73.7205	$73.72	$73.70	$73.70
Purchase #2	$223.53	11.832%	$249.9781	$249.98	$250.00	$250.00
Purchase #3	$180.99	10.827%	$200.5858	$200.59	$200.60	$200.60
Purchase #4	$117.95	10.744%	$130.6225	$130.62	$130.60	$130.60
Purchase #5	$19.54	10.376%	$21.5675	$21.57	$21.55	$21.60
Purchase #6	$205.72	8.591%	$223.3934	$223.39	$223.40	$223.40
Purchase #7	$67.86	6.522%	$72.2858	$72.29	$72.30	$72.30
7 purchase totals =	$885.93		$972.1536	$972.16	$972.15	$972.20