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	$113.44	12.607%	$127.7414	$127.74	$127.75	$127.70
Purchase #2	$175.43	12.255%	$196.9289	$196.93	$196.95	$196.90
Purchase #3	$41.60	4.590%	$43.5094	$43.51	$43.50	$43.50
Purchase #4	$97.85	11.238%	$108.8464	$108.85	$108.85	$108.80
Purchase #5	$228.28	9.277%	$249.4575	$249.46	$249.45	$249.50
Purchase #6	$57.70	4.269%	$60.1632	$60.16	$60.15	$60.20
Purchase #7	$130.57	5.378%	$137.5921	$137.59	$137.60	$137.60
7 purchase totals =	$844.87		$924.2389	$924.24	$924.25	$924.20