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	$116.34	6.497%	$123.8986	$123.90	$123.90	$123.90
Purchase #2	$37.48	9.664%	$41.1021	$41.10	$41.10	$41.10
Purchase #3	$96.82	6.643%	$103.2518	$103.25	$103.25	$103.30
Purchase #4	$71.76	13.110%	$81.1677	$81.17	$81.15	$81.20
Purchase #5	$74.84	11.302%	$83.2984	$83.30	$83.30	$83.30
Purchase #6	$113.40	11.369%	$126.2924	$126.29	$126.30	$126.30
Purchase #7	$11.98	3.677%	$12.4205	$12.42	$12.40	$12.40
7 purchase totals =	$522.62		$571.4315	$571.43	$571.40	$571.50