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	$122.94	10.829%	$136.2532	$136.25	$136.25	$136.30
Purchase #2	$43.62	11.140%	$48.4793	$48.48	$48.50	$48.50
Purchase #3	$100.58	5.246%	$105.8564	$105.86	$105.85	$105.90
Purchase #4	$167.87	11.471%	$187.1264	$187.13	$187.15	$187.10
Purchase #5	$250.82	7.789%	$270.3564	$270.36	$270.35	$270.40
Purchase #6	$79.34	5.255%	$83.5093	$83.51	$83.50	$83.50
Purchase #7	$39.88	9.791%	$43.7847	$43.78	$43.80	$43.80
7 purchase totals =	$805.05		$875.3657	$875.37	$875.40	$875.50