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	$213.47	12.562%	$240.2861	$240.29	$240.30	$240.30
Purchase #2	$57.70	3.186%	$59.5383	$59.54	$59.55	$59.50
Purchase #3	$29.49	5.112%	$30.9975	$31.00	$31.00	$31.00
Purchase #4	$82.45	10.537%	$91.1378	$91.14	$91.15	$91.10
Purchase #5	$81.64	9.543%	$89.4309	$89.43	$89.45	$89.40
Purchase #6	$203.75	9.413%	$222.929	$222.93	$222.95	$222.90
Purchase #7	$181.27	3.616%	$187.8247	$187.82	$187.80	$187.80
7 purchase totals =	$849.77		$922.1443	$922.15	$922.20	$922.00