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	$86.74	4.456%	$90.6051	$90.61	$90.60	$90.60
Purchase #2	$147.99	13.508%	$167.9805	$167.98	$168.00	$168.00
Purchase #3	$18.39	13.585%	$20.8883	$20.89	$20.90	$20.90
Purchase #4	$88.69	6.521%	$94.4735	$94.47	$94.45	$94.50
Purchase #5	$142.57	6.814%	$152.2847	$152.28	$152.30	$152.30
Purchase #6	$152.66	5.600%	$161.209	$161.21	$161.20	$161.20
Purchase #7	$104.57	6.487%	$111.3535	$111.35	$111.35	$111.40
7 purchase totals =	$741.61		$798.7946	$798.79	$798.80	$798.90