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	$248.77	7.418%	$267.2238	$267.22	$267.20	$267.20
Purchase #2	$137.72	10.681%	$152.4299	$152.43	$152.45	$152.40
Purchase #3	$94.89	11.773%	$106.0614	$106.06	$106.05	$106.10
Purchase #4	$10.83	8.142%	$11.7118	$11.71	$11.70	$11.70
Purchase #5	$215.93	10.249%	$238.0607	$238.06	$238.05	$238.10
Purchase #6	$27.36	3.677%	$28.366	$28.37	$28.35	$28.40
Purchase #7	$56.35	10.192%	$62.0932	$62.09	$62.10	$62.10
7 purchase totals =	$791.85		$865.9468	$865.94	$865.90	$866.00