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	$16.62	11.587%	$18.5458	$18.55	$18.55	$18.50
Purchase #2	$7.52	12.665%	$8.4724	$8.47	$8.45	$8.50
Purchase #3	$83.49	7.522%	$89.7701	$89.77	$89.75	$89.80
Purchase #4	$162.98	7.607%	$175.3779	$175.38	$175.40	$175.40
Purchase #5	$140.46	8.222%	$152.0086	$152.01	$152.00	$152.00
Purchase #6	$163.76	13.304%	$185.5466	$185.55	$185.55	$185.50
Purchase #7	$86.31	12.737%	$97.3033	$97.30	$97.30	$97.30
7 purchase totals =	$661.14		$727.0247	$727.03	$727.00	$727.00