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	$128.83	6.576%	$137.3019	$137.30	$137.30	$137.30
Purchase #2	$5.88	4.455%	$6.142	$6.14	$6.15	$6.10
Purchase #3	$109.80	12.522%	$123.5492	$123.55	$123.55	$123.50
Purchase #4	$162.82	10.524%	$179.9552	$179.96	$179.95	$180.00
Purchase #5	$248.37	3.624%	$257.3709	$257.37	$257.35	$257.40
Purchase #6	$105.34	10.323%	$116.2142	$116.21	$116.20	$116.20
Purchase #7	$228.61	5.364%	$240.8726	$240.87	$240.85	$240.90
7 purchase totals =	$989.65		$1,061.4060	$1,061.40	$1,061.35	$1,061.40