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	$162.42	5.820%	$171.8728	$171.87	$171.85	$171.90
Purchase #2	$124.67	12.238%	$139.9271	$139.93	$139.95	$139.90
Purchase #3	$51.31	11.636%	$57.2804	$57.28	$57.30	$57.30
Purchase #4	$94.41	10.480%	$104.3042	$104.30	$104.30	$104.30
Purchase #5	$121.69	5.650%	$128.5655	$128.57	$128.55	$128.60
Purchase #6	$151.71	12.466%	$170.6222	$170.62	$170.60	$170.60
Purchase #7	$33.62	6.272%	$35.7286	$35.73	$35.75	$35.70
7 purchase totals =	$739.83		$808.3008	$808.30	$808.30	$808.30