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	$36.57	8.855%	$39.8083	$39.81	$39.80	$39.80
Purchase #2	$108.49	8.293%	$117.4871	$117.49	$117.50	$117.50
Purchase #3	$58.78	10.287%	$64.8267	$64.83	$64.85	$64.80
Purchase #4	$86.69	13.558%	$98.4434	$98.44	$98.45	$98.40
Purchase #5	$36.57	10.740%	$40.4976	$40.50	$40.50	$40.50
Purchase #6	$41.92	4.395%	$43.7624	$43.76	$43.75	$43.80
Purchase #7	$38.33	13.713%	$43.5862	$43.59	$43.60	$43.60
7 purchase totals =	$407.35		$448.4117	$448.42	$448.45	$448.40