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	$89.92	7.418%	$96.5903	$96.59	$96.60	$96.60
Purchase #2	$13.28	13.145%	$15.0257	$15.03	$15.05	$15.00
Purchase #3	$206.78	3.229%	$213.4569	$213.46	$213.45	$213.50
Purchase #4	$131.69	10.727%	$145.8164	$145.82	$145.80	$145.80
Purchase #5	$148.94	10.835%	$165.0776	$165.08	$165.10	$165.10
Purchase #6	$31.73	6.431%	$33.7706	$33.77	$33.75	$33.80
Purchase #7	$152.56	8.586%	$165.6588	$165.66	$165.65	$165.70
7 purchase totals =	$774.90		$835.3963	$835.41	$835.40	$835.50