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	$230.75	10.609%	$255.2303	$255.23	$255.25	$255.20
Purchase #2	$211.56	5.244%	$222.6542	$222.65	$222.65	$222.70
Purchase #3	$103.49	10.154%	$113.9984	$114.00	$114.00	$114.00
Purchase #4	$86.31	3.211%	$89.0814	$89.08	$89.10	$89.10
Purchase #5	$68.93	4.408%	$71.9684	$71.97	$71.95	$72.00
Purchase #6	$154.74	8.267%	$167.5324	$167.53	$167.55	$167.50
Purchase #7	$16.53	11.774%	$18.4762	$18.48	$18.50	$18.50
7 purchase totals =	$872.31		$938.9413	$938.94	$939.00	$939.00