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	$128.42	4.474%	$134.1655	$134.17	$134.15	$134.20
Purchase #2	$159.65	6.423%	$169.9043	$169.90	$169.90	$169.90
Purchase #3	$141.90	6.311%	$150.8553	$150.86	$150.85	$150.90
Purchase #4	$107.94	5.182%	$113.5335	$113.53	$113.55	$113.50
Purchase #5	$106.52	4.526%	$111.3411	$111.34	$111.35	$111.30
Purchase #6	$157.81	4.784%	$165.3596	$165.36	$165.35	$165.40
Purchase #7	$12.91	3.382%	$13.3466	$13.35	$13.35	$13.30
7 purchase totals =	$815.15		$858.5059	$858.51	$858.50	$858.50