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	$20.64	4.744%	$21.6192	$21.62	$21.60	$21.60
Purchase #2	$244.32	13.485%	$277.2666	$277.27	$277.25	$277.30
Purchase #3	$231.58	10.193%	$255.1849	$255.18	$255.20	$255.20
Purchase #4	$116.43	12.482%	$130.9628	$130.96	$130.95	$131.00
Purchase #5	$27.54	13.567%	$31.2764	$31.28	$31.30	$31.30
Purchase #6	$220.36	3.646%	$228.3943	$228.39	$228.40	$228.40
Purchase #7	$81.74	9.827%	$89.7726	$89.77	$89.75	$89.80
7 purchase totals =	$942.61		$1,034.4768	$1,034.47	$1,034.45	$1,034.60