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	$216.66	11.843%	$242.319	$242.32	$242.30	$242.30
Purchase #2	$170.73	11.843%	$190.9496	$190.95	$190.95	$190.90
Purchase #3	$52.40	4.175%	$54.5877	$54.59	$54.60	$54.60
Purchase #4	$199.43	12.400%	$224.1593	$224.16	$224.15	$224.20
Purchase #5	$94.44	13.278%	$106.9797	$106.98	$107.00	$107.00
Purchase #6	$197.54	5.555%	$208.5133	$208.51	$208.50	$208.50
Purchase #7	$69.55	5.550%	$73.41	$73.41	$73.40	$73.40
7 purchase totals =	$1,000.75		$1,100.9186	$1,100.92	$1,100.90	$1,100.90