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	$21.62	10.592%	$23.91	$23.91	$23.90	$23.90
Purchase #2	$250.65	5.638%	$264.7816	$264.78	$264.80	$264.80
Purchase #3	$217.39	11.307%	$241.9703	$241.97	$241.95	$242.00
Purchase #4	$40.93	13.137%	$46.307	$46.31	$46.30	$46.30
Purchase #5	$90.27	12.843%	$101.8634	$101.86	$101.85	$101.90
Purchase #6	$77.53	10.700%	$85.8257	$85.83	$85.85	$85.80
Purchase #7	$243.56	7.822%	$262.6113	$262.61	$262.60	$262.60
7 purchase totals =	$941.95		$1,027.2693	$1,027.27	$1,027.25	$1,027.30