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	$123.26	5.794%	$130.4017	$130.40	$130.40	$130.40
Purchase #2	$197.75	9.113%	$215.771	$215.77	$215.75	$215.80
Purchase #3	$164.96	6.791%	$176.1624	$176.16	$176.15	$176.20
Purchase #4	$163.27	9.261%	$178.3904	$178.39	$178.40	$178.40
Purchase #5	$158.59	5.152%	$166.7606	$166.76	$166.75	$166.80
Purchase #6	$90.45	9.655%	$99.1829	$99.18	$99.20	$99.20
Purchase #7	$127.32	13.290%	$144.2408	$144.24	$144.25	$144.20
7 purchase totals =	$1,025.60		$1,110.9098	$1,110.90	$1,110.90	$1,111.00