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	$53.67	8.700%	$58.3393	$58.34	$58.35	$58.30
Purchase #2	$162.84	13.465%	$184.7664	$184.77	$184.75	$184.80
Purchase #3	$34.89	9.355%	$38.154	$38.15	$38.15	$38.20
Purchase #4	$134.31	11.592%	$149.8792	$149.88	$149.90	$149.90
Purchase #5	$13.36	9.648%	$14.649	$14.65	$14.65	$14.60
Purchase #6	$31.93	11.513%	$35.6061	$35.61	$35.60	$35.60
Purchase #7	$81.72	10.277%	$90.1184	$90.12	$90.10	$90.10
7 purchase totals =	$512.72		$571.5124	$571.52	$571.50	$571.50