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	$154.52	8.130%	$167.0825	$167.08	$167.10	$167.10
Purchase #2	$41.74	10.145%	$45.9745	$45.97	$45.95	$46.00
Purchase #3	$154.59	12.521%	$173.9462	$173.95	$173.95	$173.90
Purchase #4	$113.46	7.290%	$121.7312	$121.73	$121.75	$121.70
Purchase #5	$154.85	12.253%	$173.8238	$173.82	$173.80	$173.80
Purchase #6	$50.39	10.449%	$55.6553	$55.66	$55.65	$55.70
Purchase #7	$80.28	11.339%	$89.3829	$89.38	$89.40	$89.40
7 purchase totals =	$749.83		$827.5964	$827.59	$827.60	$827.60