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	$51.86	9.665%	$56.8723	$56.87	$56.85	$56.90
Purchase #2	$81.25	7.860%	$87.6363	$87.64	$87.65	$87.60
Purchase #3	$159.41	8.197%	$172.4768	$172.48	$172.50	$172.50
Purchase #4	$56.42	11.375%	$62.8378	$62.84	$62.85	$62.80
Purchase #5	$56.80	5.130%	$59.7138	$59.71	$59.70	$59.70
Purchase #6	$174.28	4.156%	$181.5231	$181.52	$181.50	$181.50
Purchase #7	$161.81	4.401%	$168.9313	$168.93	$168.95	$168.90
7 purchase totals =	$741.83		$789.9914	$789.99	$790.00	$789.90