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	$36.30	12.641%	$40.8887	$40.89	$40.90	$40.90
Purchase #2	$221.92	9.723%	$243.4973	$243.50	$243.50	$243.50
Purchase #3	$99.86	7.850%	$107.699	$107.70	$107.70	$107.70
Purchase #4	$57.59	3.173%	$59.4173	$59.42	$59.40	$59.40
Purchase #5	$112.44	5.137%	$118.216	$118.22	$118.20	$118.20
Purchase #6	$31.31	11.349%	$34.8634	$34.86	$34.85	$34.90
Purchase #7	$230.28	13.460%	$261.2757	$261.28	$261.30	$261.30
7 purchase totals =	$789.70		$865.8574	$865.87	$865.85	$865.90