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	$5.32	5.474%	$5.6112	$5.61	$5.60	$5.60
Purchase #2	$99.34	5.280%	$104.5852	$104.59	$104.60	$104.60
Purchase #3	$118.54	9.766%	$130.1166	$130.12	$130.10	$130.10
Purchase #4	$50.25	10.288%	$55.4197	$55.42	$55.40	$55.40
Purchase #5	$98.71	7.396%	$106.0106	$106.01	$106.00	$106.00
Purchase #6	$153.90	12.140%	$172.5835	$172.58	$172.60	$172.60
Purchase #7	$103.61	8.769%	$112.6956	$112.70	$112.70	$112.70
7 purchase totals =	$629.67		$687.0224	$687.03	$687.00	$687.00