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	$15.30	5.283%	$16.1083	$16.11	$16.10	$16.10
Purchase #2	$55.58	7.581%	$59.7935	$59.79	$59.80	$59.80
Purchase #3	$39.46	3.633%	$40.8936	$40.89	$40.90	$40.90
Purchase #4	$234.67	3.157%	$242.0785	$242.08	$242.10	$242.10
Purchase #5	$107.87	13.484%	$122.4152	$122.42	$122.40	$122.40
Purchase #6	$89.67	11.282%	$99.7866	$99.79	$99.80	$99.80
Purchase #7	$9.67	12.274%	$10.8569	$10.86	$10.85	$10.90
7 purchase totals =	$552.22		$591.9326	$591.94	$591.95	$592.00