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	$82.89	9.180%	$90.4993	$90.50	$90.50	$90.50
Purchase #2	$116.27	8.557%	$126.2192	$126.22	$126.20	$126.20
Purchase #3	$116.51	5.733%	$123.1895	$123.19	$123.20	$123.20
Purchase #4	$112.82	8.407%	$122.3048	$122.30	$122.30	$122.30
Purchase #5	$39.42	8.869%	$42.9162	$42.92	$42.90	$42.90
Purchase #6	$245.77	8.835%	$267.4838	$267.48	$267.50	$267.50
Purchase #7	$197.64	6.432%	$210.3522	$210.35	$210.35	$210.40
7 purchase totals =	$911.32		$982.9650	$982.96	$982.95	$983.00