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	$127.48	10.770%	$141.2096	$141.21	$141.20	$141.20
Purchase #2	$37.59	3.700%	$38.9808	$38.98	$39.00	$39.00
Purchase #3	$87.78	9.695%	$96.2903	$96.29	$96.30	$96.30
Purchase #4	$242.47	9.710%	$266.0138	$266.01	$266.00	$266.00
Purchase #5	$13.38	12.546%	$15.0587	$15.06	$15.05	$15.10
Purchase #6	$96.47	5.603%	$101.8752	$101.88	$101.90	$101.90
Purchase #7	$6.39	13.733%	$7.2675	$7.27	$7.25	$7.30
7 purchase totals =	$611.56		$666.6959	$666.70	$666.70	$666.80