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	$88.60	13.602%	$100.6514	$100.65	$100.65	$100.70
Purchase #2	$168.28	10.726%	$186.3297	$186.33	$186.35	$186.30
Purchase #3	$74.47	10.253%	$82.1054	$82.11	$82.10	$82.10
Purchase #4	$208.77	10.661%	$231.027	$231.03	$231.05	$231.00
Purchase #5	$97.62	3.621%	$101.1548	$101.15	$101.15	$101.20
Purchase #6	$18.71	7.465%	$20.1067	$20.11	$20.10	$20.10
Purchase #7	$86.62	3.568%	$89.7106	$89.71	$89.70	$89.70
7 purchase totals =	$743.07		$811.0856	$811.09	$811.10	$811.10