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	$104.25	4.773%	$109.2259	$109.23	$109.25	$109.20
Purchase #2	$134.97	7.714%	$145.3816	$145.38	$145.40	$145.40
Purchase #3	$9.32	12.801%	$10.5131	$10.51	$10.50	$10.50
Purchase #4	$216.49	12.236%	$242.9797	$242.98	$243.00	$243.00
Purchase #5	$246.89	5.338%	$260.069	$260.07	$260.05	$260.10
Purchase #6	$100.76	10.280%	$111.1181	$111.12	$111.10	$111.10
Purchase #7	$44.49	5.237%	$46.8199	$46.82	$46.80	$46.80
7 purchase totals =	$857.17		$926.1073	$926.11	$926.10	$926.10