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	$61.32	10.405%	$67.7003	$67.70	$67.70	$67.70
Purchase #2	$73.54	12.265%	$82.5597	$82.56	$82.55	$82.60
Purchase #3	$29.54	11.784%	$33.021	$33.02	$33.00	$33.00
Purchase #4	$32.43	8.291%	$35.1188	$35.12	$35.10	$35.10
Purchase #5	$228.39	5.302%	$240.4992	$240.50	$240.50	$240.50
Purchase #6	$29.73	4.870%	$31.1779	$31.18	$31.20	$31.20
Purchase #7	$82.38	10.636%	$91.1419	$91.14	$91.15	$91.10
7 purchase totals =	$537.33		$581.2188	$581.22	$581.20	$581.20