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	$57.43	13.650%	$65.2692	$65.27	$65.25	$65.30
Purchase #2	$203.58	7.285%	$218.4108	$218.41	$218.40	$218.40
Purchase #3	$227.95	12.364%	$256.1337	$256.13	$256.15	$256.10
Purchase #4	$72.78	11.495%	$81.1461	$81.15	$81.15	$81.10
Purchase #5	$53.60	3.221%	$55.3265	$55.33	$55.35	$55.30
Purchase #6	$185.54	10.675%	$205.3464	$205.35	$205.35	$205.30
Purchase #7	$14.89	3.221%	$15.3696	$15.37	$15.35	$15.40
7 purchase totals =	$815.77		$897.0023	$897.01	$897.00	$896.90