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	$88.96	3.175%	$91.7845	$91.78	$91.80	$91.80
Purchase #2	$144.59	3.800%	$150.0844	$150.08	$150.10	$150.10
Purchase #3	$15.80	6.618%	$16.8456	$16.85	$16.85	$16.80
Purchase #4	$39.56	6.579%	$42.1627	$42.16	$42.15	$42.20
Purchase #5	$134.83	10.502%	$148.9898	$148.99	$149.00	$149.00
Purchase #6	$57.86	11.495%	$64.511	$64.51	$64.50	$64.50
Purchase #7	$64.69	11.783%	$72.3124	$72.31	$72.30	$72.30
7 purchase totals =	$546.29		$586.6904	$586.68	$586.70	$586.70