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	$62.51	9.354%	$68.3572	$68.36	$68.35	$68.40
Purchase #2	$131.42	4.529%	$137.372	$137.37	$137.35	$137.40
Purchase #3	$151.34	5.514%	$159.6849	$159.68	$159.70	$159.70
Purchase #4	$73.85	11.616%	$82.4284	$82.43	$82.45	$82.40
Purchase #5	$39.76	5.624%	$41.9961	$42.00	$42.00	$42.00
Purchase #6	$205.47	13.832%	$233.8906	$233.89	$233.90	$233.90
Purchase #7	$5.30	10.686%	$5.8664	$5.87	$5.85	$5.90
7 purchase totals =	$669.65		$729.5956	$729.60	$729.60	$729.70