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	$9.72	11.114%	$10.8003	$10.80	$10.80	$10.80
Purchase #2	$84.83	6.557%	$90.3923	$90.39	$90.40	$90.40
Purchase #3	$241.79	3.730%	$250.8088	$250.81	$250.80	$250.80
Purchase #4	$233.51	11.337%	$259.983	$259.98	$260.00	$260.00
Purchase #5	$99.38	6.406%	$105.7463	$105.75	$105.75	$105.70
Purchase #6	$67.30	7.323%	$72.2284	$72.23	$72.25	$72.20
Purchase #7	$170.43	11.767%	$190.4845	$190.48	$190.50	$190.50
7 purchase totals =	$906.96		$980.4436	$980.44	$980.50	$980.40