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	$54.35	6.126%	$57.6795	$57.68	$57.70	$57.70
Purchase #2	$140.25	5.559%	$148.0465	$148.05	$148.05	$148.00
Purchase #3	$240.70	9.842%	$264.3897	$264.39	$264.40	$264.40
Purchase #4	$150.89	11.588%	$168.3751	$168.38	$168.40	$168.40
Purchase #5	$108.82	3.404%	$112.5242	$112.52	$112.50	$112.50
Purchase #6	$232.98	13.304%	$263.9757	$263.98	$264.00	$264.00
Purchase #7	$34.43	11.384%	$38.3495	$38.35	$38.35	$38.30
7 purchase totals =	$962.42		$1,053.3402	$1,053.35	$1,053.40	$1,053.30