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	$10.51	13.331%	$11.9111	$11.91	$11.90	$11.90
Purchase #2	$32.92	3.212%	$33.9774	$33.98	$34.00	$34.00
Purchase #3	$102.73	6.869%	$109.7865	$109.79	$109.80	$109.80
Purchase #4	$16.33	13.211%	$18.4874	$18.49	$18.50	$18.50
Purchase #5	$72.47	6.263%	$77.0088	$77.01	$77.00	$77.00
Purchase #6	$51.96	3.123%	$53.5827	$53.58	$53.60	$53.60
Purchase #7	$102.88	3.523%	$106.5045	$106.50	$106.50	$106.50
7 purchase totals =	$389.80		$411.2584	$411.26	$411.30	$411.30