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	$97.79	5.452%	$103.1215	$103.12	$103.10	$103.10
Purchase #2	$220.59	9.790%	$242.1858	$242.19	$242.20	$242.20
Purchase #3	$37.25	7.637%	$40.0948	$40.09	$40.10	$40.10
Purchase #4	$35.46	4.123%	$36.922	$36.92	$36.90	$36.90
Purchase #5	$105.85	6.155%	$112.3651	$112.37	$112.35	$112.40
Purchase #6	$52.58	5.676%	$55.5644	$55.56	$55.55	$55.60
Purchase #7	$32.69	6.761%	$34.9002	$34.90	$34.90	$34.90
7 purchase totals =	$582.21		$625.1538	$625.15	$625.10	$625.20