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	$38.98	11.603%	$43.5028	$43.50	$43.50	$43.50
Purchase #2	$175.45	5.355%	$184.8453	$184.85	$184.85	$184.80
Purchase #3	$62.34	8.822%	$67.8396	$67.84	$67.85	$67.80
Purchase #4	$108.61	3.682%	$112.609	$112.61	$112.60	$112.60
Purchase #5	$18.59	10.172%	$20.481	$20.48	$20.50	$20.50
Purchase #6	$53.51	7.864%	$57.718	$57.72	$57.70	$57.70
Purchase #7	$98.41	4.377%	$102.7174	$102.72	$102.70	$102.70
7 purchase totals =	$555.89		$589.7131	$589.72	$589.70	$589.60