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	$25.45	12.661%	$28.6722	$28.67	$28.65	$28.70
Purchase #2	$29.41	4.799%	$30.8214	$30.82	$30.80	$30.80
Purchase #3	$66.73	8.295%	$72.2653	$72.27	$72.25	$72.30
Purchase #4	$170.73	9.811%	$187.4803	$187.48	$187.50	$187.50
Purchase #5	$223.58	4.230%	$233.0374	$233.04	$233.05	$233.00
Purchase #6	$79.61	13.512%	$90.3669	$90.37	$90.35	$90.40
Purchase #7	$27.26	4.151%	$28.3916	$28.39	$28.40	$28.40
7 purchase totals =	$622.77		$671.0351	$671.04	$671.00	$671.10