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	$30.54	4.834%	$32.0163	$32.02	$32.00	$32.00
Purchase #2	$59.99	12.769%	$67.6501	$67.65	$67.65	$67.70
Purchase #3	$43.64	3.344%	$45.0993	$45.10	$45.10	$45.10
Purchase #4	$153.52	7.813%	$165.5145	$165.51	$165.50	$165.50
Purchase #5	$22.43	4.163%	$23.3638	$23.36	$23.35	$23.40
Purchase #6	$155.26	10.788%	$172.0094	$172.01	$172.00	$172.00
Purchase #7	$131.94	8.325%	$142.924	$142.92	$142.90	$142.90
7 purchase totals =	$597.32		$648.5774	$648.57	$648.50	$648.60