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	$151.36	10.658%	$167.4919	$167.49	$167.50	$167.50
Purchase #2	$78.52	5.488%	$82.8292	$82.83	$82.85	$82.80
Purchase #3	$46.97	4.800%	$49.2246	$49.22	$49.20	$49.20
Purchase #4	$131.82	5.776%	$139.4339	$139.43	$139.45	$139.40
Purchase #5	$147.99	4.341%	$154.4142	$154.41	$154.40	$154.40
Purchase #6	$30.62	3.410%	$31.6641	$31.66	$31.65	$31.70
Purchase #7	$193.50	13.277%	$219.191	$219.19	$219.20	$219.20
7 purchase totals =	$780.78		$844.2489	$844.23	$844.25	$844.20