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	$232.54	13.209%	$263.2562	$263.26	$263.25	$263.30
Purchase #2	$205.97	10.580%	$227.7616	$227.76	$227.75	$227.80
Purchase #3	$70.61	10.501%	$78.0248	$78.02	$78.00	$78.00
Purchase #4	$39.97	8.695%	$43.4454	$43.45	$43.45	$43.40
Purchase #5	$162.41	7.646%	$174.8279	$174.83	$174.85	$174.80
Purchase #6	$59.96	3.789%	$62.2319	$62.23	$62.25	$62.20
Purchase #7	$50.56	6.803%	$53.9996	$54.00	$54.00	$54.00
7 purchase totals =	$822.02		$903.5474	$903.55	$903.55	$903.50