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	$101.45	10.666%	$112.2707	$112.27	$112.25	$112.30
Purchase #2	$123.94	8.605%	$134.605	$134.61	$134.60	$134.60
Purchase #3	$43.38	4.612%	$45.3807	$45.38	$45.40	$45.40
Purchase #4	$222.75	4.616%	$233.0321	$233.03	$233.05	$233.00
Purchase #5	$8.96	12.765%	$10.1037	$10.10	$10.10	$10.10
Purchase #6	$232.97	3.133%	$240.269	$240.27	$240.25	$240.30
Purchase #7	$92.90	11.653%	$103.7256	$103.73	$103.75	$103.70
7 purchase totals =	$826.35		$879.3868	$879.39	$879.40	$879.40