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	$90.89	13.600%	$103.251	$103.25	$103.25	$103.30
Purchase #2	$135.50	4.430%	$141.5027	$141.50	$141.50	$141.50
Purchase #3	$162.83	13.615%	$184.9993	$185.00	$185.00	$185.00
Purchase #4	$125.76	8.540%	$136.4999	$136.50	$136.50	$136.50
Purchase #5	$158.70	7.139%	$170.0296	$170.03	$170.05	$170.00
Purchase #6	$156.28	6.297%	$166.121	$166.12	$166.10	$166.10
Purchase #7	$34.96	9.453%	$38.2648	$38.26	$38.25	$38.30
7 purchase totals =	$864.92		$940.6683	$940.66	$940.65	$940.70