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	$123.42	6.271%	$131.1597	$131.16	$131.15	$131.20
Purchase #2	$184.87	13.842%	$210.4597	$210.46	$210.45	$210.50
Purchase #3	$18.91	3.571%	$19.5853	$19.59	$19.60	$19.60
Purchase #4	$71.60	12.818%	$80.7777	$80.78	$80.80	$80.80
Purchase #5	$211.41	7.160%	$226.547	$226.55	$226.55	$226.50
Purchase #6	$154.72	9.733%	$169.7789	$169.78	$169.80	$169.80
Purchase #7	$17.89	7.506%	$19.2328	$19.23	$19.25	$19.20
7 purchase totals =	$782.82		$857.5411	$857.55	$857.60	$857.60