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	$49.90	7.571%	$53.6779	$53.68	$53.70	$53.70
Purchase #2	$42.30	8.320%	$45.8194	$45.82	$45.80	$45.80
Purchase #3	$78.86	4.422%	$82.3472	$82.35	$82.35	$82.30
Purchase #4	$87.54	3.453%	$90.5628	$90.56	$90.55	$90.60
Purchase #5	$50.49	6.257%	$53.6492	$53.65	$53.65	$53.60
Purchase #6	$244.32	13.206%	$276.5849	$276.58	$276.60	$276.60
Purchase #7	$31.63	5.188%	$33.271	$33.27	$33.25	$33.30
7 purchase totals =	$585.04		$635.9124	$635.91	$635.90	$635.90