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	$145.95	9.626%	$159.9991	$160.00	$160.00	$160.00
Purchase #2	$204.83	12.602%	$230.6427	$230.64	$230.65	$230.60
Purchase #3	$79.48	11.446%	$88.5773	$88.58	$88.60	$88.60
Purchase #4	$178.77	3.614%	$185.2307	$185.23	$185.25	$185.20
Purchase #5	$78.91	8.300%	$85.4595	$85.46	$85.45	$85.50
Purchase #6	$136.40	4.740%	$142.8654	$142.87	$142.85	$142.90
Purchase #7	$6.86	10.627%	$7.589	$7.59	$7.60	$7.60
7 purchase totals =	$831.20		$900.3637	$900.37	$900.40	$900.40