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	$165.90	7.829%	$178.8883	$178.89	$178.90	$178.90
Purchase #2	$36.97	13.854%	$42.0918	$42.09	$42.10	$42.10
Purchase #3	$233.88	13.761%	$266.0642	$266.06	$266.05	$266.10
Purchase #4	$43.75	3.789%	$45.4077	$45.41	$45.40	$45.40
Purchase #5	$64.85	9.111%	$70.7585	$70.76	$70.75	$70.80
Purchase #6	$144.78	12.181%	$162.4157	$162.42	$162.40	$162.40
Purchase #7	$53.92	3.446%	$55.7781	$55.78	$55.80	$55.80
7 purchase totals =	$744.05		$821.4043	$821.41	$821.40	$821.50