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	$70.98	11.191%	$78.9234	$78.92	$78.90	$78.90
Purchase #2	$226.46	3.210%	$233.7294	$233.73	$233.75	$233.70
Purchase #3	$164.95	7.284%	$176.965	$176.97	$176.95	$177.00
Purchase #4	$6.81	13.522%	$7.7308	$7.73	$7.75	$7.70
Purchase #5	$154.59	5.344%	$162.8513	$162.85	$162.85	$162.90
Purchase #6	$89.82	6.740%	$95.8739	$95.87	$95.85	$95.90
Purchase #7	$57.32	6.516%	$61.055	$61.06	$61.05	$61.10
7 purchase totals =	$770.93		$817.1288	$817.13	$817.10	$817.20