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	$5.65	5.325%	$5.9509	$5.95	$5.95	$6.00
Purchase #2	$61.48	8.148%	$66.4894	$66.49	$66.50	$66.50
Purchase #3	$145.71	3.715%	$151.1231	$151.12	$151.10	$151.10
Purchase #4	$250.56	11.611%	$279.6525	$279.65	$279.65	$279.70
Purchase #5	$6.94	11.225%	$7.719	$7.72	$7.70	$7.70
Purchase #6	$72.63	8.385%	$78.72	$78.72	$78.70	$78.70
Purchase #7	$248.92	12.771%	$280.7096	$280.71	$280.70	$280.70
7 purchase totals =	$791.89		$870.3645	$870.36	$870.30	$870.40