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	$26.41	6.380%	$28.095	$28.10	$28.10	$28.10
Purchase #2	$46.63	8.174%	$50.4415	$50.44	$50.45	$50.40
Purchase #3	$88.61	13.163%	$100.2737	$100.27	$100.25	$100.30
Purchase #4	$176.56	4.183%	$183.9455	$183.95	$183.95	$183.90
Purchase #5	$118.32	8.578%	$128.4695	$128.47	$128.45	$128.50
Purchase #6	$167.50	7.794%	$180.555	$180.56	$180.55	$180.60
Purchase #7	$100.65	12.678%	$113.4104	$113.41	$113.40	$113.40
7 purchase totals =	$724.68		$785.1906	$785.20	$785.15	$785.20