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	$234.30	6.640%	$249.8575	$249.86	$249.85	$249.90
Purchase #2	$147.66	10.130%	$162.618	$162.62	$162.60	$162.60
Purchase #3	$87.55	3.285%	$90.426	$90.43	$90.45	$90.40
Purchase #4	$12.76	10.810%	$14.1394	$14.14	$14.15	$14.10
Purchase #5	$246.59	3.663%	$255.6226	$255.62	$255.60	$255.60
Purchase #6	$84.35	12.799%	$95.146	$95.15	$95.15	$95.10
Purchase #7	$6.78	4.143%	$7.0609	$7.06	$7.05	$7.10
7 purchase totals =	$819.99		$874.8704	$874.88	$874.85	$874.80