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	$173.30	6.867%	$185.2005	$185.20	$185.20	$185.20
Purchase #2	$235.33	10.787%	$260.715	$260.72	$260.70	$260.70
Purchase #3	$30.69	13.474%	$34.8252	$34.83	$34.85	$34.80
Purchase #4	$10.65	11.582%	$11.8835	$11.88	$11.90	$11.90
Purchase #5	$92.61	13.374%	$104.9957	$105.00	$105.00	$105.00
Purchase #6	$173.42	11.367%	$193.1327	$193.13	$193.15	$193.10
Purchase #7	$113.31	9.306%	$123.8546	$123.85	$123.85	$123.90
7 purchase totals =	$829.31		$914.6072	$914.61	$914.65	$914.60