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	$242.35	5.782%	$256.3627	$256.36	$256.35	$256.40
Purchase #2	$58.35	9.476%	$63.8792	$63.88	$63.90	$63.90
Purchase #3	$150.48	5.312%	$158.4735	$158.47	$158.45	$158.50
Purchase #4	$83.81	6.349%	$89.1311	$89.13	$89.15	$89.10
Purchase #5	$61.63	5.715%	$65.1522	$65.15	$65.15	$65.20
Purchase #6	$249.59	12.183%	$279.9975	$280.00	$280.00	$280.00
Purchase #7	$236.75	3.118%	$244.1319	$244.13	$244.15	$244.10
7 purchase totals =	$1,082.96		$1,157.1281	$1,157.12	$1,157.15	$1,157.20