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	$6.76	12.542%	$7.6078	$7.61	$7.60	$7.60
Purchase #2	$7.38	6.534%	$7.8622	$7.86	$7.85	$7.90
Purchase #3	$43.90	6.328%	$46.678	$46.68	$46.70	$46.70
Purchase #4	$60.60	8.558%	$65.7861	$65.79	$65.80	$65.80
Purchase #5	$83.70	6.619%	$89.2401	$89.24	$89.25	$89.20
Purchase #6	$77.41	6.304%	$82.2899	$82.29	$82.30	$82.30
Purchase #7	$249.88	12.335%	$280.7027	$280.70	$280.70	$280.70
7 purchase totals =	$529.63		$580.1668	$580.17	$580.20	$580.20