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	$49.41	9.747%	$54.226	$54.23	$54.25	$54.20
Purchase #2	$64.67	12.677%	$72.8682	$72.87	$72.85	$72.90
Purchase #3	$45.34	4.674%	$47.4592	$47.46	$47.45	$47.50
Purchase #4	$105.98	10.833%	$117.4608	$117.46	$117.45	$117.50
Purchase #5	$95.62	10.388%	$105.553	$105.55	$105.55	$105.60
Purchase #6	$156.57	11.805%	$175.0531	$175.05	$175.05	$175.10
Purchase #7	$81.65	9.282%	$89.2288	$89.23	$89.25	$89.20
7 purchase totals =	$599.24		$661.8491	$661.85	$661.85	$662.00