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	$134.72	9.484%	$147.4968	$147.50	$147.50	$147.50
Purchase #2	$203.83	13.400%	$231.1432	$231.14	$231.15	$231.10
Purchase #3	$168.53	7.641%	$181.4074	$181.41	$181.40	$181.40
Purchase #4	$203.90	9.184%	$222.6262	$222.63	$222.65	$222.60
Purchase #5	$174.38	11.325%	$194.1285	$194.13	$194.15	$194.10
Purchase #6	$144.51	6.111%	$153.341	$153.34	$153.35	$153.30
Purchase #7	$172.98	7.223%	$185.4743	$185.47	$185.45	$185.50
7 purchase totals =	$1,202.85		$1,315.6174	$1,315.62	$1,315.65	$1,315.50