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	$127.28	3.164%	$131.3071	$131.31	$131.30	$131.30
Purchase #2	$67.87	4.190%	$70.7138	$70.71	$70.70	$70.70
Purchase #3	$203.68	3.198%	$210.1937	$210.19	$210.20	$210.20
Purchase #4	$249.28	3.743%	$258.6106	$258.61	$258.60	$258.60
Purchase #5	$107.75	4.300%	$112.3833	$112.38	$112.40	$112.40
Purchase #6	$62.44	5.239%	$65.7112	$65.71	$65.70	$65.70
Purchase #7	$123.43	4.794%	$129.3472	$129.35	$129.35	$129.30
7 purchase totals =	$941.73		$978.2669	$978.26	$978.25	$978.20