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	$99.39	11.799%	$111.117	$111.12	$111.10	$111.10
Purchase #2	$89.51	6.137%	$95.0032	$95.00	$95.00	$95.00
Purchase #3	$234.82	3.244%	$242.4376	$242.44	$242.45	$242.40
Purchase #4	$64.93	6.272%	$69.0024	$69.00	$69.00	$69.00
Purchase #5	$24.86	8.781%	$27.043	$27.04	$27.05	$27.00
Purchase #6	$37.60	6.467%	$40.0316	$40.03	$40.05	$40.00
Purchase #7	$52.50	5.375%	$55.3219	$55.32	$55.30	$55.30
7 purchase totals =	$603.61		$639.9567	$639.95	$639.95	$639.80