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	$105.53	12.356%	$118.5693	$118.57	$118.55	$118.60
Purchase #2	$30.49	8.624%	$33.1195	$33.12	$33.10	$33.10
Purchase #3	$117.79	12.518%	$132.535	$132.54	$132.55	$132.50
Purchase #4	$72.27	9.286%	$78.981	$78.98	$79.00	$79.00
Purchase #5	$90.56	3.658%	$93.8727	$93.87	$93.85	$93.90
Purchase #6	$33.73	5.506%	$35.5872	$35.59	$35.60	$35.60
Purchase #7	$61.94	4.614%	$64.7979	$64.80	$64.80	$64.80
7 purchase totals =	$512.31		$557.4626	$557.47	$557.45	$557.50