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	$139.85	13.297%	$158.4459	$158.45	$158.45	$158.40
Purchase #2	$213.33	11.765%	$238.4283	$238.43	$238.45	$238.40
Purchase #3	$165.26	10.732%	$182.9957	$183.00	$183.00	$183.00
Purchase #4	$190.84	7.674%	$205.4851	$205.49	$205.50	$205.50
Purchase #5	$162.72	6.487%	$173.2756	$173.28	$173.30	$173.30
Purchase #6	$20.72	5.560%	$21.872	$21.87	$21.85	$21.90
Purchase #7	$186.36	6.704%	$198.8536	$198.85	$198.85	$198.90
7 purchase totals =	$1,079.08		$1,179.3562	$1,179.37	$1,179.40	$1,179.40