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	$124.91	13.591%	$141.8865	$141.89	$141.90	$141.90
Purchase #2	$184.62	8.503%	$200.3182	$200.32	$200.30	$200.30
Purchase #3	$162.70	9.367%	$177.9401	$177.94	$177.95	$177.90
Purchase #4	$28.76	11.759%	$32.1419	$32.14	$32.15	$32.10
Purchase #5	$19.60	5.280%	$20.6349	$20.63	$20.65	$20.60
Purchase #6	$12.52	8.652%	$13.6032	$13.60	$13.60	$13.60
Purchase #7	$30.76	10.219%	$33.9034	$33.90	$33.90	$33.90
7 purchase totals =	$563.87		$620.4282	$620.42	$620.45	$620.30