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	$38.34	5.182%	$40.3268	$40.33	$40.35	$40.30
Purchase #2	$99.38	13.291%	$112.5886	$112.59	$112.60	$112.60
Purchase #3	$249.81	12.832%	$281.8656	$281.87	$281.85	$281.90
Purchase #4	$219.30	8.738%	$238.4624	$238.46	$238.45	$238.50
Purchase #5	$235.33	13.313%	$266.6595	$266.66	$266.65	$266.70
Purchase #6	$79.62	8.738%	$86.5772	$86.58	$86.60	$86.60
Purchase #7	$189.72	5.642%	$200.424	$200.42	$200.40	$200.40
7 purchase totals =	$1,111.50		$1,226.9041	$1,226.91	$1,226.90	$1,227.00