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	$64.29	12.187%	$72.125	$72.13	$72.15	$72.10
Purchase #2	$187.43	11.339%	$208.6827	$208.68	$208.70	$208.70
Purchase #3	$129.53	10.172%	$142.7058	$142.71	$142.70	$142.70
Purchase #4	$153.53	11.765%	$171.5928	$171.59	$171.60	$171.60
Purchase #5	$118.54	7.657%	$127.6166	$127.62	$127.60	$127.60
Purchase #6	$180.62	7.514%	$194.1918	$194.19	$194.20	$194.20
Purchase #7	$59.50	13.351%	$67.4438	$67.44	$67.45	$67.40
7 purchase totals =	$893.44		$984.3585	$984.36	$984.40	$984.30