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	$42.93	3.787%	$44.5558	$44.56	$44.55	$44.60
Purchase #2	$98.73	10.245%	$108.8449	$108.84	$108.85	$108.80
Purchase #3	$129.85	10.547%	$143.5453	$143.55	$143.55	$143.50
Purchase #4	$99.96	12.455%	$112.41	$112.41	$112.40	$112.40
Purchase #5	$196.45	3.599%	$203.5202	$203.52	$203.50	$203.50
Purchase #6	$137.52	11.417%	$153.2207	$153.22	$153.20	$153.20
Purchase #7	$18.58	10.458%	$20.5231	$20.52	$20.50	$20.50
7 purchase totals =	$724.02		$786.6200	$786.62	$786.55	$786.50