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	$49.96	13.123%	$56.5163	$56.52	$56.50	$56.50
Purchase #2	$71.76	13.169%	$81.2101	$81.21	$81.20	$81.20
Purchase #3	$89.47	12.300%	$100.4748	$100.47	$100.45	$100.50
Purchase #4	$202.59	13.450%	$229.8384	$229.84	$229.85	$229.80
Purchase #5	$198.61	3.190%	$204.9457	$204.95	$204.95	$204.90
Purchase #6	$124.29	13.330%	$140.8579	$140.86	$140.85	$140.90
Purchase #7	$117.86	4.359%	$122.9975	$123.00	$123.00	$123.00
7 purchase totals =	$854.54		$936.8407	$936.85	$936.80	$936.80