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	$169.44	6.732%	$180.8467	$180.85	$180.85	$180.80
Purchase #2	$39.72	4.198%	$41.3874	$41.39	$41.40	$41.40
Purchase #3	$12.55	10.736%	$13.8974	$13.90	$13.90	$13.90
Purchase #4	$103.66	6.569%	$110.4694	$110.47	$110.45	$110.50
Purchase #5	$160.58	13.262%	$181.8761	$181.88	$181.90	$181.90
Purchase #6	$152.77	6.509%	$162.7138	$162.71	$162.70	$162.70
Purchase #7	$83.97	7.295%	$90.0956	$90.10	$90.10	$90.10
7 purchase totals =	$722.69		$781.2864	$781.30	$781.30	$781.30