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	$155.68	8.432%	$168.8069	$168.81	$168.80	$168.80
Purchase #2	$100.45	6.175%	$106.6528	$106.65	$106.65	$106.70
Purchase #3	$91.27	12.351%	$102.5428	$102.54	$102.55	$102.50
Purchase #4	$119.80	5.615%	$126.5268	$126.53	$126.55	$126.50
Purchase #5	$190.73	10.588%	$210.9245	$210.92	$210.90	$210.90
Purchase #6	$117.56	7.472%	$126.3441	$126.34	$126.35	$126.30
Purchase #7	$228.38	13.346%	$258.8596	$258.86	$258.85	$258.90
7 purchase totals =	$1,003.87		$1,100.6575	$1,100.65	$1,100.65	$1,100.60