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	$64.72	13.497%	$73.4553	$73.46	$73.45	$73.50
Purchase #2	$113.46	9.587%	$124.3374	$124.34	$124.35	$124.30
Purchase #3	$59.89	10.577%	$66.2246	$66.22	$66.20	$66.20
Purchase #4	$98.44	5.348%	$103.7046	$103.70	$103.70	$103.70
Purchase #5	$86.46	10.384%	$95.438	$95.44	$95.45	$95.40
Purchase #6	$22.90	6.223%	$24.3251	$24.33	$24.35	$24.30
Purchase #7	$96.82	9.219%	$105.7458	$105.75	$105.75	$105.70
7 purchase totals =	$542.69		$593.2308	$593.24	$593.25	$593.10