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	$50.69	11.470%	$56.5041	$56.50	$56.50	$56.50
Purchase #2	$165.48	13.728%	$188.1971	$188.20	$188.20	$188.20
Purchase #3	$59.59	9.716%	$65.3798	$65.38	$65.40	$65.40
Purchase #4	$249.53	12.421%	$280.5241	$280.52	$280.50	$280.50
Purchase #5	$75.84	11.345%	$84.444	$84.44	$84.45	$84.40
Purchase #6	$40.44	8.163%	$43.7411	$43.74	$43.75	$43.70
Purchase #7	$160.28	7.401%	$172.1423	$172.14	$172.15	$172.10
7 purchase totals =	$801.85		$890.9325	$890.92	$890.95	$890.80