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	$213.97	3.274%	$220.9754	$220.98	$221.00	$221.00
Purchase #2	$48.37	5.752%	$51.1522	$51.15	$51.15	$51.20
Purchase #3	$164.40	4.674%	$172.0841	$172.08	$172.10	$172.10
Purchase #4	$13.85	9.151%	$15.1174	$15.12	$15.10	$15.10
Purchase #5	$149.33	12.853%	$168.5234	$168.52	$168.50	$168.50
Purchase #6	$184.98	10.113%	$203.687	$203.69	$203.70	$203.70
Purchase #7	$89.78	12.128%	$100.6685	$100.67	$100.65	$100.70
7 purchase totals =	$864.68		$932.2080	$932.21	$932.20	$932.30