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	$99.65	6.615%	$106.2418	$106.24	$106.25	$106.20
Purchase #2	$197.79	12.116%	$221.7542	$221.75	$221.75	$221.80
Purchase #3	$133.33	4.324%	$139.0952	$139.10	$139.10	$139.10
Purchase #4	$96.88	7.155%	$103.8118	$103.81	$103.80	$103.80
Purchase #5	$36.89	9.179%	$40.2761	$40.28	$40.30	$40.30
Purchase #6	$44.80	8.479%	$48.5986	$48.60	$48.60	$48.60
Purchase #7	$105.34	4.252%	$109.8191	$109.82	$109.80	$109.80
7 purchase totals =	$714.68		$769.5968	$769.60	$769.60	$769.60