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	$145.55	9.662%	$159.613	$159.61	$159.60	$159.60
Purchase #2	$162.99	6.137%	$172.9927	$172.99	$173.00	$173.00
Purchase #3	$80.57	10.804%	$89.2748	$89.27	$89.25	$89.30
Purchase #4	$148.96	13.665%	$169.3154	$169.32	$169.30	$169.30
Purchase #5	$35.42	12.170%	$39.7306	$39.73	$39.75	$39.70
Purchase #6	$63.98	13.760%	$72.7836	$72.78	$72.80	$72.80
Purchase #7	$112.79	5.671%	$119.1863	$119.19	$119.20	$119.20
7 purchase totals =	$750.26		$822.8964	$822.89	$822.90	$822.90