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	$56.73	12.620%	$63.8893	$63.89	$63.90	$63.90
Purchase #2	$124.45	13.572%	$141.3404	$141.34	$141.35	$141.30
Purchase #3	$84.99	5.203%	$89.412	$89.41	$89.40	$89.40
Purchase #4	$127.52	3.797%	$132.3619	$132.36	$132.35	$132.40
Purchase #5	$39.35	3.756%	$40.828	$40.83	$40.85	$40.80
Purchase #6	$139.42	12.256%	$156.5073	$156.51	$156.50	$156.50
Purchase #7	$75.44	5.303%	$79.4406	$79.44	$79.45	$79.40
7 purchase totals =	$647.90		$703.7795	$703.78	$703.80	$703.70