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	$34.72	7.665%	$37.3813	$37.38	$37.40	$37.40
Purchase #2	$138.94	4.595%	$145.3243	$145.32	$145.30	$145.30
Purchase #3	$198.87	12.490%	$223.7089	$223.71	$223.70	$223.70
Purchase #4	$141.73	6.291%	$150.6462	$150.65	$150.65	$150.60
Purchase #5	$85.28	5.441%	$89.9201	$89.92	$89.90	$89.90
Purchase #6	$208.88	6.500%	$222.4572	$222.46	$222.45	$222.50
Purchase #7	$205.48	6.811%	$219.4752	$219.48	$219.50	$219.50
7 purchase totals =	$1,013.90		$1,088.9132	$1,088.92	$1,088.90	$1,088.90