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	$92.61	3.843%	$96.169	$96.17	$96.15	$96.20
Purchase #2	$142.42	5.596%	$150.3898	$150.39	$150.40	$150.40
Purchase #3	$96.33	7.772%	$103.8168	$103.82	$103.80	$103.80
Purchase #4	$76.96	13.755%	$87.5458	$87.55	$87.55	$87.50
Purchase #5	$16.69	13.242%	$18.9001	$18.90	$18.90	$18.90
Purchase #6	$100.33	13.212%	$113.5856	$113.59	$113.60	$113.60
Purchase #7	$78.55	13.521%	$89.1707	$89.17	$89.15	$89.20
7 purchase totals =	$603.89		$659.5778	$659.59	$659.55	$659.60