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	$99.52	11.553%	$111.0175	$111.02	$111.00	$111.00
Purchase #2	$154.71	3.166%	$159.6081	$159.61	$159.60	$159.60
Purchase #3	$171.97	4.671%	$180.0027	$180.00	$180.00	$180.00
Purchase #4	$166.94	3.552%	$172.8697	$172.87	$172.85	$172.90
Purchase #5	$220.72	7.230%	$236.6781	$236.68	$236.70	$236.70
Purchase #6	$105.73	7.717%	$113.8892	$113.89	$113.90	$113.90
Purchase #7	$86.79	5.146%	$91.2562	$91.26	$91.25	$91.30
7 purchase totals =	$1,006.38		$1,065.3215	$1,065.33	$1,065.30	$1,065.40