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	$152.58	8.246%	$165.1617	$165.16	$165.15	$165.20
Purchase #2	$93.52	10.709%	$103.5351	$103.54	$103.55	$103.50
Purchase #3	$16.48	6.198%	$17.5014	$17.50	$17.50	$17.50
Purchase #4	$107.77	6.132%	$114.3785	$114.38	$114.40	$114.40
Purchase #5	$33.52	6.834%	$35.8108	$35.81	$35.80	$35.80
Purchase #6	$185.97	5.612%	$196.4066	$196.41	$196.40	$196.40
Purchase #7	$164.40	12.585%	$185.0897	$185.09	$185.10	$185.10
7 purchase totals =	$754.24		$817.8838	$817.89	$817.90	$817.90