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	$29.90	8.122%	$32.3285	$32.33	$32.35	$32.30
Purchase #2	$105.93	9.129%	$115.6003	$115.60	$115.60	$115.60
Purchase #3	$147.87	10.105%	$162.8123	$162.81	$162.80	$162.80
Purchase #4	$174.33	10.764%	$193.0949	$193.09	$193.10	$193.10
Purchase #5	$41.61	9.755%	$45.6691	$45.67	$45.65	$45.70
Purchase #6	$101.58	7.833%	$109.5368	$109.54	$109.55	$109.50
Purchase #7	$70.51	12.788%	$79.5268	$79.53	$79.55	$79.50
7 purchase totals =	$671.73		$738.5687	$738.57	$738.60	$738.50