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	$156.34	10.109%	$172.1444	$172.14	$172.15	$172.10
Purchase #2	$29.94	3.522%	$30.9945	$30.99	$31.00	$31.00
Purchase #3	$233.81	3.838%	$242.7836	$242.78	$242.80	$242.80
Purchase #4	$106.80	4.764%	$111.888	$111.89	$111.90	$111.90
Purchase #5	$172.50	4.842%	$180.8525	$180.85	$180.85	$180.90
Purchase #6	$128.41	5.310%	$135.2286	$135.23	$135.25	$135.20
Purchase #7	$219.31	3.252%	$226.442	$226.44	$226.45	$226.40
7 purchase totals =	$1,047.11		$1,100.3336	$1,100.32	$1,100.40	$1,100.30