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	$75.26	4.675%	$78.7784	$78.78	$78.80	$78.80
Purchase #2	$226.84	5.655%	$239.6678	$239.67	$239.65	$239.70
Purchase #3	$158.96	3.274%	$164.1644	$164.16	$164.15	$164.20
Purchase #4	$199.56	11.314%	$222.1382	$222.14	$222.15	$222.10
Purchase #5	$47.31	4.431%	$49.4063	$49.41	$49.40	$49.40
Purchase #6	$20.80	3.616%	$21.5521	$21.55	$21.55	$21.60
Purchase #7	$61.71	8.670%	$67.0603	$67.06	$67.05	$67.10
7 purchase totals =	$790.44		$842.7675	$842.77	$842.75	$842.90