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	$78.69	10.127%	$86.6589	$86.66	$86.65	$86.70
Purchase #2	$240.69	12.815%	$271.5344	$271.53	$271.55	$271.50
Purchase #3	$137.31	11.772%	$153.4741	$153.47	$153.45	$153.50
Purchase #4	$107.50	12.331%	$120.7558	$120.76	$120.75	$120.80
Purchase #5	$87.76	3.335%	$90.6868	$90.69	$90.70	$90.70
Purchase #6	$191.35	12.150%	$214.599	$214.60	$214.60	$214.60
Purchase #7	$57.39	3.867%	$59.6093	$59.61	$59.60	$59.60
7 purchase totals =	$900.69		$997.3183	$997.32	$997.30	$997.40