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	$35.68	9.182%	$38.9561	$38.96	$38.95	$39.00
Purchase #2	$174.26	11.621%	$194.5108	$194.51	$194.50	$194.50
Purchase #3	$171.34	9.234%	$187.1615	$187.16	$187.15	$187.20
Purchase #4	$18.37	9.518%	$20.1185	$20.12	$20.10	$20.10
Purchase #5	$144.66	5.447%	$152.5396	$152.54	$152.55	$152.50
Purchase #6	$202.75	9.760%	$222.5384	$222.54	$222.55	$222.50
Purchase #7	$86.50	6.156%	$91.8249	$91.82	$91.80	$91.80
7 purchase totals =	$833.56		$907.6498	$907.65	$907.60	$907.60