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	$247.27	4.589%	$258.6172	$258.62	$258.60	$258.60
Purchase #2	$86.29	10.194%	$95.0864	$95.09	$95.10	$95.10
Purchase #3	$129.52	12.673%	$145.9341	$145.93	$145.95	$145.90
Purchase #4	$38.96	3.276%	$40.2363	$40.24	$40.25	$40.20
Purchase #5	$165.33	8.726%	$179.7567	$179.76	$179.75	$179.80
Purchase #6	$82.77	3.694%	$85.8275	$85.83	$85.85	$85.80
Purchase #7	$190.92	6.577%	$203.4768	$203.48	$203.50	$203.50
7 purchase totals =	$941.06		$1,008.9350	$1,008.95	$1,009.00	$1,008.90