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	$16.27	3.671%	$16.8673	$16.87	$16.85	$16.90
Purchase #2	$247.58	13.245%	$280.372	$280.37	$280.35	$280.40
Purchase #3	$222.57	9.225%	$243.1021	$243.10	$243.10	$243.10
Purchase #4	$86.31	4.357%	$90.0705	$90.07	$90.05	$90.10
Purchase #5	$194.98	12.287%	$218.9372	$218.94	$218.95	$218.90
Purchase #6	$60.96	8.663%	$66.241	$66.24	$66.25	$66.20
Purchase #7	$52.36	6.134%	$55.5718	$55.57	$55.55	$55.60
7 purchase totals =	$881.03		$971.1619	$971.16	$971.10	$971.20