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	$71.59	12.262%	$80.3684	$80.37	$80.35	$80.40
Purchase #2	$50.64	5.170%	$53.2581	$53.26	$53.25	$53.30
Purchase #3	$135.87	7.143%	$145.5752	$145.58	$145.60	$145.60
Purchase #4	$246.59	7.181%	$264.2976	$264.30	$264.30	$264.30
Purchase #5	$143.60	8.655%	$156.0286	$156.03	$156.05	$156.00
Purchase #6	$196.51	10.155%	$216.4656	$216.47	$216.45	$216.50
Purchase #7	$233.83	4.315%	$243.9198	$243.92	$243.90	$243.90
7 purchase totals =	$1,078.63		$1,159.9133	$1,159.93	$1,159.90	$1,160.00