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	$18.45	10.739%	$20.4313	$20.43	$20.45	$20.40
Purchase #2	$211.70	3.226%	$218.5294	$218.53	$218.55	$218.50
Purchase #3	$103.59	9.219%	$113.14	$113.14	$113.15	$113.10
Purchase #4	$101.93	10.670%	$112.8059	$112.81	$112.80	$112.80
Purchase #5	$248.54	8.659%	$270.0611	$270.06	$270.05	$270.10
Purchase #6	$53.60	10.489%	$59.2221	$59.22	$59.20	$59.20
Purchase #7	$83.65	6.478%	$89.0688	$89.07	$89.05	$89.10
7 purchase totals =	$821.46		$883.2586	$883.26	$883.25	$883.20