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	$51.45	12.375%	$57.8169	$57.82	$57.80	$57.80
Purchase #2	$18.27	10.602%	$20.207	$20.21	$20.20	$20.20
Purchase #3	$44.53	9.855%	$48.9184	$48.92	$48.90	$48.90
Purchase #4	$45.33	6.575%	$48.3104	$48.31	$48.30	$48.30
Purchase #5	$53.66	13.828%	$61.0801	$61.08	$61.10	$61.10
Purchase #6	$34.53	7.607%	$37.1567	$37.16	$37.15	$37.20
Purchase #7	$131.58	7.869%	$141.934	$141.93	$141.95	$141.90
7 purchase totals =	$379.35		$415.4235	$415.43	$415.40	$415.40