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	$117.66	8.243%	$127.3587	$127.36	$127.35	$127.40
Purchase #2	$248.64	13.195%	$281.448	$281.45	$281.45	$281.40
Purchase #3	$248.56	11.537%	$277.2364	$277.24	$277.25	$277.20
Purchase #4	$104.43	7.717%	$112.4889	$112.49	$112.50	$112.50
Purchase #5	$53.90	9.259%	$58.8906	$58.89	$58.90	$58.90
Purchase #6	$98.44	6.822%	$105.1556	$105.16	$105.15	$105.20
Purchase #7	$40.50	5.188%	$42.6011	$42.60	$42.60	$42.60
7 purchase totals =	$912.13		$1,005.1793	$1,005.19	$1,005.20	$1,005.20