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	$143.43	3.387%	$148.288	$148.29	$148.30	$148.30
Purchase #2	$250.49	9.256%	$273.6754	$273.68	$273.70	$273.70
Purchase #3	$7.36	6.778%	$7.8589	$7.86	$7.85	$7.90
Purchase #4	$104.89	7.446%	$112.7001	$112.70	$112.70	$112.70
Purchase #5	$19.61	6.456%	$20.876	$20.88	$20.90	$20.90
Purchase #6	$142.34	11.264%	$158.3732	$158.37	$158.35	$158.40
Purchase #7	$18.92	10.102%	$20.8313	$20.83	$20.85	$20.80
7 purchase totals =	$687.04		$742.6029	$742.61	$742.65	$742.70