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	$243.54	6.727%	$259.9229	$259.92	$259.90	$259.90
Purchase #2	$101.89	8.402%	$110.4508	$110.45	$110.45	$110.50
Purchase #3	$206.49	3.756%	$214.2458	$214.25	$214.25	$214.20
Purchase #4	$36.89	11.286%	$41.0534	$41.05	$41.05	$41.10
Purchase #5	$139.57	10.665%	$154.4551	$154.46	$154.45	$154.50
Purchase #6	$99.80	9.761%	$109.5415	$109.54	$109.55	$109.50
Purchase #7	$75.53	8.599%	$82.0248	$82.02	$82.00	$82.00
7 purchase totals =	$903.71		$971.6943	$971.69	$971.65	$971.70