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	$20.69	3.639%	$21.4429	$21.44	$21.45	$21.40
Purchase #2	$78.47	9.298%	$85.7661	$85.77	$85.75	$85.80
Purchase #3	$214.93	9.561%	$235.4795	$235.48	$235.50	$235.50
Purchase #4	$38.35	10.200%	$42.2617	$42.26	$42.25	$42.30
Purchase #5	$47.92	10.607%	$53.0029	$53.00	$53.00	$53.00
Purchase #6	$22.80	10.814%	$25.2656	$25.27	$25.25	$25.30
Purchase #7	$20.81	8.203%	$22.517	$22.52	$22.50	$22.50
7 purchase totals =	$443.97		$485.7357	$485.74	$485.70	$485.80