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	$162.91	4.394%	$170.0683	$170.07	$170.05	$170.10
Purchase #2	$187.86	4.755%	$196.7927	$196.79	$196.80	$196.80
Purchase #3	$182.91	13.453%	$207.5169	$207.52	$207.50	$207.50
Purchase #4	$36.91	4.698%	$38.644	$38.64	$38.65	$38.60
Purchase #5	$128.54	7.861%	$138.6445	$138.64	$138.65	$138.60
Purchase #6	$72.27	9.171%	$78.8979	$78.90	$78.90	$78.90
Purchase #7	$37.67	9.631%	$41.298	$41.30	$41.30	$41.30
7 purchase totals =	$809.07		$871.8623	$871.86	$871.85	$871.80