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	$31.79	10.606%	$35.1616	$35.16	$35.15	$35.20
Purchase #2	$234.89	10.563%	$259.7014	$259.70	$259.70	$259.70
Purchase #3	$151.54	3.496%	$156.8378	$156.84	$156.85	$156.80
Purchase #4	$79.52	12.648%	$89.5777	$89.58	$89.60	$89.60
Purchase #5	$38.60	6.253%	$41.0137	$41.01	$41.00	$41.00
Purchase #6	$113.43	4.263%	$118.2655	$118.27	$118.25	$118.30
Purchase #7	$76.36	6.851%	$81.5914	$81.59	$81.60	$81.60
7 purchase totals =	$726.13		$782.1491	$782.15	$782.15	$782.20