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	$8.75	12.557%	$9.8487	$9.85	$9.85	$9.80
Purchase #2	$44.95	11.750%	$50.2316	$50.23	$50.25	$50.20
Purchase #3	$80.71	12.150%	$90.5163	$90.52	$90.50	$90.50
Purchase #4	$50.34	7.313%	$54.0214	$54.02	$54.00	$54.00
Purchase #5	$74.49	7.539%	$80.1058	$80.11	$80.10	$80.10
Purchase #6	$146.90	11.823%	$164.268	$164.27	$164.25	$164.30
Purchase #7	$193.44	6.258%	$205.5455	$205.55	$205.55	$205.50
7 purchase totals =	$599.58		$654.5373	$654.55	$654.50	$654.40