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	$249.29	4.138%	$259.6056	$259.61	$259.60	$259.60
Purchase #2	$131.72	6.662%	$140.4952	$140.50	$140.50	$140.50
Purchase #3	$238.96	6.555%	$254.6238	$254.62	$254.60	$254.60
Purchase #4	$112.78	13.104%	$127.5587	$127.56	$127.55	$127.60
Purchase #5	$154.51	10.733%	$171.0936	$171.09	$171.10	$171.10
Purchase #6	$225.59	7.719%	$243.0033	$243.00	$243.00	$243.00
Purchase #7	$93.93	11.141%	$104.3947	$104.39	$104.40	$104.40
7 purchase totals =	$1,206.78		$1,300.7749	$1,300.77	$1,300.75	$1,300.80