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	$5.48	12.377%	$6.1583	$6.16	$6.15	$6.20
Purchase #2	$241.57	6.729%	$257.8252	$257.83	$257.85	$257.80
Purchase #3	$80.44	6.419%	$85.6034	$85.60	$85.60	$85.60
Purchase #4	$69.50	4.220%	$72.4329	$72.43	$72.45	$72.40
Purchase #5	$116.48	11.379%	$129.7343	$129.73	$129.75	$129.70
Purchase #6	$86.29	4.446%	$90.1265	$90.13	$90.15	$90.10
Purchase #7	$111.70	4.831%	$117.0962	$117.10	$117.10	$117.10
7 purchase totals =	$711.46		$758.9768	$758.98	$759.05	$758.90