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	$132.43	3.536%	$137.1127	$137.11	$137.10	$137.10
Purchase #2	$72.72	11.345%	$80.9701	$80.97	$80.95	$81.00
Purchase #3	$130.35	5.796%	$137.9051	$137.91	$137.90	$137.90
Purchase #4	$202.69	11.136%	$225.2616	$225.26	$225.25	$225.30
Purchase #5	$189.63	3.602%	$196.4605	$196.46	$196.45	$196.50
Purchase #6	$37.46	9.685%	$41.088	$41.09	$41.10	$41.10
Purchase #7	$237.81	4.472%	$248.4449	$248.44	$248.45	$248.40
7 purchase totals =	$1,003.09		$1,067.2429	$1,067.24	$1,067.20	$1,067.30