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	$245.52	13.659%	$279.0556	$279.06	$279.05	$279.10
Purchase #2	$234.70	8.804%	$255.363	$255.36	$255.35	$255.40
Purchase #3	$156.75	13.520%	$177.9426	$177.94	$177.95	$177.90
Purchase #4	$146.89	4.440%	$153.4119	$153.41	$153.40	$153.40
Purchase #5	$196.48	10.163%	$216.4483	$216.45	$216.45	$216.40
Purchase #6	$48.56	11.127%	$53.9633	$53.96	$53.95	$54.00
Purchase #7	$172.84	7.555%	$185.8981	$185.90	$185.90	$185.90
7 purchase totals =	$1,201.74		$1,322.0828	$1,322.08	$1,322.05	$1,322.10