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	$121.84	13.298%	$138.0423	$138.04	$138.05	$138.00
Purchase #2	$183.38	4.165%	$191.0178	$191.02	$191.00	$191.00
Purchase #3	$160.81	3.128%	$165.8401	$165.84	$165.85	$165.80
Purchase #4	$113.86	11.201%	$126.6135	$126.61	$126.60	$126.60
Purchase #5	$79.88	13.238%	$90.4545	$90.45	$90.45	$90.50
Purchase #6	$83.68	5.671%	$88.4255	$88.43	$88.45	$88.40
Purchase #7	$32.93	7.125%	$35.2763	$35.28	$35.30	$35.30
7 purchase totals =	$776.38		$835.6700	$835.67	$835.70	$835.60