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	$167.83	6.515%	$178.7641	$178.76	$178.75	$178.80
Purchase #2	$248.89	11.731%	$278.0873	$278.09	$278.10	$278.10
Purchase #3	$43.70	11.421%	$48.691	$48.69	$48.70	$48.70
Purchase #4	$159.51	3.211%	$164.6319	$164.63	$164.65	$164.60
Purchase #5	$110.54	7.505%	$118.836	$118.84	$118.85	$118.80
Purchase #6	$38.25	10.521%	$42.2743	$42.27	$42.25	$42.30
Purchase #7	$85.25	5.772%	$90.1706	$90.17	$90.15	$90.20
7 purchase totals =	$853.97		$921.4552	$921.45	$921.45	$921.50