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	$66.78	6.227%	$70.9384	$70.94	$70.95	$70.90
Purchase #2	$243.80	9.266%	$266.3905	$266.39	$266.40	$266.40
Purchase #3	$197.31	11.212%	$219.4324	$219.43	$219.45	$219.40
Purchase #4	$61.38	3.494%	$63.5246	$63.52	$63.50	$63.50
Purchase #5	$87.56	3.261%	$90.4153	$90.42	$90.40	$90.40
Purchase #6	$176.86	6.474%	$188.3099	$188.31	$188.30	$188.30
Purchase #7	$249.69	9.279%	$272.8587	$272.86	$272.85	$272.90
7 purchase totals =	$1,083.38		$1,171.8698	$1,171.87	$1,171.85	$1,171.80