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	$124.42	10.605%	$137.6147	$137.61	$137.60	$137.60
Purchase #2	$156.36	7.551%	$168.1667	$168.17	$168.15	$168.20
Purchase #3	$41.49	3.201%	$42.8181	$42.82	$42.80	$42.80
Purchase #4	$181.28	13.224%	$205.2525	$205.25	$205.25	$205.30
Purchase #5	$79.85	11.589%	$89.1038	$89.10	$89.10	$89.10
Purchase #6	$71.71	5.483%	$75.6419	$75.64	$75.65	$75.60
Purchase #7	$33.31	3.113%	$34.3469	$34.35	$34.35	$34.30
7 purchase totals =	$688.42		$752.9446	$752.94	$752.90	$752.90