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	$98.28	13.192%	$111.2451	$111.25	$111.25	$111.20
Purchase #2	$138.89	11.868%	$155.3735	$155.37	$155.35	$155.40
Purchase #3	$236.77	11.702%	$264.4768	$264.48	$264.50	$264.50
Purchase #4	$14.65	9.229%	$16.002	$16.00	$16.00	$16.00
Purchase #5	$38.93	10.161%	$42.8857	$42.89	$42.90	$42.90
Purchase #6	$156.55	10.264%	$172.6183	$172.62	$172.60	$172.60
Purchase #7	$155.63	5.506%	$164.199	$164.20	$164.20	$164.20
7 purchase totals =	$839.70		$926.8004	$926.81	$926.80	$926.80