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	$208.56	12.152%	$233.9042	$233.90	$233.90	$233.90
Purchase #2	$155.89	9.398%	$170.5405	$170.54	$170.55	$170.50
Purchase #3	$38.80	3.402%	$40.12	$40.12	$40.10	$40.10
Purchase #4	$10.56	7.490%	$11.3509	$11.35	$11.35	$11.40
Purchase #5	$148.96	7.566%	$160.2303	$160.23	$160.25	$160.20
Purchase #6	$242.42	13.812%	$275.9031	$275.90	$275.90	$275.90
Purchase #7	$84.94	6.268%	$90.264	$90.26	$90.25	$90.30
7 purchase totals =	$890.13		$982.3130	$982.30	$982.30	$982.30