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	$49.34	13.132%	$55.8193	$55.82	$55.80	$55.80
Purchase #2	$123.49	3.781%	$128.1592	$128.16	$128.15	$128.20
Purchase #3	$231.63	10.121%	$255.0733	$255.07	$255.05	$255.10
Purchase #4	$187.36	11.459%	$208.8296	$208.83	$208.85	$208.80
Purchase #5	$199.83	12.865%	$225.5381	$225.54	$225.55	$225.50
Purchase #6	$105.87	6.543%	$112.7971	$112.80	$112.80	$112.80
Purchase #7	$38.72	3.476%	$40.0659	$40.07	$40.05	$40.10
7 purchase totals =	$936.24		$1,026.2825	$1,026.29	$1,026.25	$1,026.30