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	$162.77	3.357%	$168.2342	$168.23	$168.25	$168.20
Purchase #2	$49.49	12.822%	$55.8356	$55.84	$55.85	$55.80
Purchase #3	$77.72	13.856%	$88.4889	$88.49	$88.50	$88.50
Purchase #4	$41.34	9.563%	$45.2933	$45.29	$45.30	$45.30
Purchase #5	$238.79	13.759%	$271.6451	$271.65	$271.65	$271.60
Purchase #6	$161.93	4.684%	$169.5148	$169.51	$169.50	$169.50
Purchase #7	$49.54	7.554%	$53.2823	$53.28	$53.30	$53.30
7 purchase totals =	$781.58		$852.2942	$852.29	$852.35	$852.20