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	$79.67	12.192%	$89.3834	$89.38	$89.40	$89.40
Purchase #2	$35.70	7.769%	$38.4735	$38.47	$38.45	$38.50
Purchase #3	$249.34	10.622%	$275.8249	$275.82	$275.80	$275.80
Purchase #4	$24.64	4.707%	$25.7998	$25.80	$25.80	$25.80
Purchase #5	$89.39	3.260%	$92.3041	$92.30	$92.30	$92.30
Purchase #6	$46.65	10.289%	$51.4498	$51.45	$51.45	$51.40
Purchase #7	$173.47	7.424%	$186.3484	$186.35	$186.35	$186.30
7 purchase totals =	$698.86		$759.5839	$759.57	$759.55	$759.50