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	$67.86	4.723%	$71.065	$71.07	$71.05	$71.10
Purchase #2	$176.77	12.213%	$198.3589	$198.36	$198.35	$198.40
Purchase #3	$59.98	7.189%	$64.292	$64.29	$64.30	$64.30
Purchase #4	$123.52	12.217%	$138.6104	$138.61	$138.60	$138.60
Purchase #5	$168.50	11.481%	$187.8455	$187.85	$187.85	$187.80
Purchase #6	$241.59	13.320%	$273.7698	$273.77	$273.75	$273.80
Purchase #7	$196.27	10.131%	$216.1541	$216.15	$216.15	$216.20
7 purchase totals =	$1,034.49		$1,150.0957	$1,150.10	$1,150.05	$1,150.20