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	$82.54	7.847%	$89.0169	$89.02	$89.00	$89.00
Purchase #2	$48.31	13.598%	$54.8792	$54.88	$54.90	$54.90
Purchase #3	$92.63	12.104%	$103.8419	$103.84	$103.85	$103.80
Purchase #4	$224.99	11.727%	$251.3746	$251.37	$251.35	$251.40
Purchase #5	$47.84	6.695%	$51.0429	$51.04	$51.05	$51.00
Purchase #6	$49.39	6.436%	$52.5687	$52.57	$52.55	$52.60
Purchase #7	$68.86	4.752%	$72.1322	$72.13	$72.15	$72.10
7 purchase totals =	$614.56		$674.8564	$674.85	$674.85	$674.80