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	$41.39	3.187%	$42.7091	$42.71	$42.70	$42.70
Purchase #2	$96.42	9.871%	$105.9376	$105.94	$105.95	$105.90
Purchase #3	$15.92	11.211%	$17.7048	$17.70	$17.70	$17.70
Purchase #4	$178.84	6.630%	$190.6971	$190.70	$190.70	$190.70
Purchase #5	$168.59	13.859%	$191.9549	$191.95	$191.95	$192.00
Purchase #6	$97.47	12.467%	$109.6216	$109.62	$109.60	$109.60
Purchase #7	$54.67	3.330%	$56.4905	$56.49	$56.50	$56.50
7 purchase totals =	$653.30		$715.1156	$715.11	$715.10	$715.10