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	$25.42	8.558%	$27.5954	$27.60	$27.60	$27.60
Purchase #2	$162.81	4.660%	$170.3969	$170.40	$170.40	$170.40
Purchase #3	$182.49	7.811%	$196.7443	$196.74	$196.75	$196.70
Purchase #4	$126.37	13.843%	$143.8634	$143.86	$143.85	$143.90
Purchase #5	$84.94	7.673%	$91.4574	$91.46	$91.45	$91.50
Purchase #6	$38.82	10.165%	$42.7661	$42.77	$42.75	$42.80
Purchase #7	$32.80	3.282%	$33.8765	$33.88	$33.90	$33.90
7 purchase totals =	$653.65		$706.7000	$706.71	$706.70	$706.80