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	$144.83	6.642%	$154.4496	$154.45	$154.45	$154.40
Purchase #2	$202.94	11.142%	$225.5516	$225.55	$225.55	$225.60
Purchase #3	$223.59	8.751%	$243.1564	$243.16	$243.15	$243.20
Purchase #4	$71.75	12.874%	$80.9871	$80.99	$81.00	$81.00
Purchase #5	$199.86	7.662%	$215.1733	$215.17	$215.15	$215.20
Purchase #6	$47.71	10.763%	$52.845	$52.85	$52.85	$52.80
Purchase #7	$37.57	12.591%	$42.3004	$42.30	$42.30	$42.30
7 purchase totals =	$928.25		$1,014.4634	$1,014.47	$1,014.45	$1,014.50