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	$125.42	5.106%	$131.8239	$131.82	$131.80	$131.80
Purchase #2	$118.25	12.530%	$133.0667	$133.07	$133.05	$133.10
Purchase #3	$213.33	7.549%	$229.4343	$229.43	$229.45	$229.40
Purchase #4	$144.44	7.674%	$155.5243	$155.52	$155.50	$155.50
Purchase #5	$239.76	9.746%	$263.127	$263.13	$263.15	$263.10
Purchase #6	$141.61	3.535%	$146.6159	$146.62	$146.60	$146.60
Purchase #7	$102.31	13.624%	$116.2487	$116.25	$116.25	$116.20
7 purchase totals =	$1,085.12		$1,175.8408	$1,175.84	$1,175.80	$1,175.70