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	$243.35	13.367%	$275.8786	$275.88	$275.90	$275.90
Purchase #2	$93.37	7.268%	$100.1561	$100.16	$100.15	$100.20
Purchase #3	$164.35	9.373%	$179.7545	$179.75	$179.75	$179.80
Purchase #4	$37.29	11.662%	$41.6388	$41.64	$41.65	$41.60
Purchase #5	$38.82	7.812%	$41.8526	$41.85	$41.85	$41.90
Purchase #6	$184.90	12.789%	$208.5469	$208.55	$208.55	$208.50
Purchase #7	$77.88	3.828%	$80.8612	$80.86	$80.85	$80.90
7 purchase totals =	$839.96		$928.6887	$928.69	$928.70	$928.80