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	$96.75	3.295%	$99.9379	$99.94	$99.95	$99.90
Purchase #2	$10.49	8.835%	$11.4168	$11.42	$11.40	$11.40
Purchase #3	$160.57	6.646%	$171.2415	$171.24	$171.25	$171.20
Purchase #4	$97.62	6.154%	$103.6275	$103.63	$103.65	$103.60
Purchase #5	$20.77	3.601%	$21.5179	$21.52	$21.50	$21.50
Purchase #6	$21.79	7.497%	$23.4236	$23.42	$23.40	$23.40
Purchase #7	$25.46	7.329%	$27.326	$27.33	$27.35	$27.30
7 purchase totals =	$433.45		$458.4912	$458.50	$458.50	$458.30