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	$93.79	5.654%	$99.0929	$99.09	$99.10	$99.10
Purchase #2	$134.86	4.603%	$141.0676	$141.07	$141.05	$141.10
Purchase #3	$67.33	7.709%	$72.5205	$72.52	$72.50	$72.50
Purchase #4	$20.47	11.800%	$22.8855	$22.89	$22.90	$22.90
Purchase #5	$40.46	10.665%	$44.7751	$44.78	$44.80	$44.80
Purchase #6	$6.42	12.273%	$7.2079	$7.21	$7.20	$7.20
Purchase #7	$48.55	6.314%	$51.6154	$51.62	$51.60	$51.60
7 purchase totals =	$411.88		$439.1649	$439.18	$439.15	$439.20