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	$113.87	8.440%	$123.4806	$123.48	$123.50	$123.50
Purchase #2	$112.92	4.471%	$117.9687	$117.97	$117.95	$118.00
Purchase #3	$71.95	10.249%	$79.3242	$79.32	$79.30	$79.30
Purchase #4	$143.64	12.337%	$161.3609	$161.36	$161.35	$161.40
Purchase #5	$33.72	11.862%	$37.7199	$37.72	$37.70	$37.70
Purchase #6	$92.35	8.187%	$99.9107	$99.91	$99.90	$99.90
Purchase #7	$162.90	4.440%	$170.1328	$170.13	$170.15	$170.10
7 purchase totals =	$731.35		$789.8978	$789.89	$789.85	$789.90