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	$155.81	7.552%	$167.5768	$167.58	$167.60	$167.60
Purchase #2	$132.56	5.211%	$139.4677	$139.47	$139.45	$139.50
Purchase #3	$114.67	7.727%	$123.5306	$123.53	$123.55	$123.50
Purchase #4	$26.87	7.265%	$28.8221	$28.82	$28.80	$28.80
Purchase #5	$49.73	5.313%	$52.3722	$52.37	$52.35	$52.40
Purchase #6	$26.57	12.308%	$29.8402	$29.84	$29.85	$29.80
Purchase #7	$226.57	10.485%	$250.3259	$250.33	$250.35	$250.30
7 purchase totals =	$732.78		$791.9355	$791.94	$791.95	$791.90