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	$20.69	5.136%	$21.7526	$21.75	$21.75	$21.80
Purchase #2	$51.34	5.525%	$54.1765	$54.18	$54.20	$54.20
Purchase #3	$149.27	12.766%	$168.3258	$168.33	$168.35	$168.30
Purchase #4	$101.81	12.300%	$114.3326	$114.33	$114.35	$114.30
Purchase #5	$72.40	7.248%	$77.6476	$77.65	$77.65	$77.60
Purchase #6	$73.27	6.595%	$78.1022	$78.10	$78.10	$78.10
Purchase #7	$248.79	9.752%	$273.052	$273.05	$273.05	$273.10
7 purchase totals =	$717.57		$787.3893	$787.39	$787.45	$787.40