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	$94.89	8.109%	$102.5846	$102.58	$102.60	$102.60
Purchase #2	$213.90	10.866%	$237.1424	$237.14	$237.15	$237.10
Purchase #3	$104.88	10.137%	$115.5117	$115.51	$115.50	$115.50
Purchase #4	$86.58	5.873%	$91.6648	$91.66	$91.65	$91.70
Purchase #5	$121.80	7.734%	$131.22	$131.22	$131.20	$131.20
Purchase #6	$40.35	11.739%	$45.0867	$45.09	$45.10	$45.10
Purchase #7	$88.81	13.302%	$100.6235	$100.62	$100.60	$100.60
7 purchase totals =	$751.21		$823.8337	$823.82	$823.80	$823.80