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	$126.58	8.446%	$137.2709	$137.27	$137.25	$137.30
Purchase #2	$151.34	9.590%	$165.8535	$165.85	$165.85	$165.90
Purchase #3	$199.59	11.295%	$222.1337	$222.13	$222.15	$222.10
Purchase #4	$198.43	9.287%	$216.8582	$216.86	$216.85	$216.90
Purchase #5	$79.31	12.337%	$89.0945	$89.09	$89.10	$89.10
Purchase #6	$234.38	7.805%	$252.6734	$252.67	$252.65	$252.70
Purchase #7	$162.27	13.494%	$184.1667	$184.17	$184.15	$184.20
7 purchase totals =	$1,151.90		$1,268.0509	$1,268.04	$1,268.00	$1,268.20