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	$240.59	10.215%	$265.1663	$265.17	$265.15	$265.20
Purchase #2	$241.96	9.872%	$265.8463	$265.85	$265.85	$265.80
Purchase #3	$143.82	6.296%	$152.8749	$152.87	$152.85	$152.90
Purchase #4	$110.42	3.654%	$114.4547	$114.45	$114.45	$114.50
Purchase #5	$37.37	12.828%	$42.1638	$42.16	$42.15	$42.20
Purchase #6	$198.35	5.802%	$209.8583	$209.86	$209.85	$209.90
Purchase #7	$146.98	8.325%	$159.2161	$159.22	$159.20	$159.20
7 purchase totals =	$1,119.49		$1,209.5804	$1,209.58	$1,209.50	$1,209.70