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	$35.56	12.282%	$39.9275	$39.93	$39.95	$39.90
Purchase #2	$99.27	3.311%	$102.5568	$102.56	$102.55	$102.60
Purchase #3	$166.95	6.352%	$177.5547	$177.55	$177.55	$177.60
Purchase #4	$233.94	8.447%	$253.7009	$253.70	$253.70	$253.70
Purchase #5	$121.96	4.395%	$127.3201	$127.32	$127.30	$127.30
Purchase #6	$241.80	11.359%	$269.2661	$269.27	$269.25	$269.30
Purchase #7	$115.89	12.662%	$130.564	$130.56	$130.55	$130.60
7 purchase totals =	$1,015.37		$1,100.8901	$1,100.89	$1,100.85	$1,101.00