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	$241.81	6.767%	$258.1733	$258.17	$258.15	$258.20
Purchase #2	$166.43	13.141%	$188.3006	$188.30	$188.30	$188.30
Purchase #3	$110.66	12.860%	$124.8909	$124.89	$124.90	$124.90
Purchase #4	$39.76	6.402%	$42.3054	$42.31	$42.30	$42.30
Purchase #5	$60.94	12.357%	$68.4704	$68.47	$68.45	$68.50
Purchase #6	$19.63	7.510%	$21.1042	$21.10	$21.10	$21.10
Purchase #7	$133.29	11.300%	$148.3518	$148.35	$148.35	$148.40
7 purchase totals =	$772.52		$851.5966	$851.59	$851.55	$851.70