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	$143.25	12.230%	$160.7695	$160.77	$160.75	$160.80
Purchase #2	$98.73	7.223%	$105.8613	$105.86	$105.85	$105.90
Purchase #3	$23.72	3.254%	$24.4918	$24.49	$24.50	$24.50
Purchase #4	$70.53	9.484%	$77.2191	$77.22	$77.20	$77.20
Purchase #5	$175.45	7.430%	$188.4859	$188.49	$188.50	$188.50
Purchase #6	$86.34	3.296%	$89.1858	$89.19	$89.20	$89.20
Purchase #7	$39.69	10.693%	$43.9341	$43.93	$43.95	$43.90
7 purchase totals =	$637.71		$689.9475	$689.95	$689.95	$690.00