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	$96.52	3.559%	$99.9551	$99.96	$99.95	$100.00
Purchase #2	$88.47	12.292%	$99.3447	$99.34	$99.35	$99.30
Purchase #3	$215.58	12.173%	$241.8226	$241.82	$241.80	$241.80
Purchase #4	$193.64	8.709%	$210.5041	$210.50	$210.50	$210.50
Purchase #5	$22.80	4.493%	$23.8244	$23.82	$23.80	$23.80
Purchase #6	$80.45	8.849%	$87.569	$87.57	$87.55	$87.60
Purchase #7	$85.37	4.743%	$89.4191	$89.42	$89.40	$89.40
7 purchase totals =	$782.83		$852.4390	$852.43	$852.35	$852.40