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	$70.61	10.604%	$78.0975	$78.10	$78.10	$78.10
Purchase #2	$137.40	12.282%	$154.2755	$154.28	$154.30	$154.30
Purchase #3	$142.66	9.585%	$156.334	$156.33	$156.35	$156.30
Purchase #4	$107.35	4.585%	$112.272	$112.27	$112.25	$112.30
Purchase #5	$115.62	13.724%	$131.4877	$131.49	$131.50	$131.50
Purchase #6	$32.69	8.597%	$35.5004	$35.50	$35.50	$35.50
Purchase #7	$130.84	5.343%	$137.8308	$137.83	$137.85	$137.80
7 purchase totals =	$737.17		$805.7979	$805.80	$805.85	$805.80