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	$97.56	3.334%	$100.8127	$100.81	$100.80	$100.80
Purchase #2	$83.55	6.647%	$89.1036	$89.10	$89.10	$89.10
Purchase #3	$87.93	5.220%	$92.5199	$92.52	$92.50	$92.50
Purchase #4	$162.65	8.760%	$176.8981	$176.90	$176.90	$176.90
Purchase #5	$229.71	13.816%	$261.4467	$261.45	$261.45	$261.40
Purchase #6	$145.48	10.540%	$160.8136	$160.81	$160.80	$160.80
Purchase #7	$240.66	12.399%	$270.4994	$270.50	$270.50	$270.50
7 purchase totals =	$1,047.54		$1,152.0940	$1,152.09	$1,152.05	$1,152.00