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	$150.72	11.678%	$168.3211	$168.32	$168.30	$168.30
Purchase #2	$243.93	12.173%	$273.6236	$273.62	$273.60	$273.60
Purchase #3	$88.79	7.476%	$95.4279	$95.43	$95.45	$95.40
Purchase #4	$228.40	7.291%	$245.0526	$245.05	$245.05	$245.10
Purchase #5	$211.68	13.665%	$240.6061	$240.61	$240.60	$240.60
Purchase #6	$200.63	10.654%	$222.0051	$222.01	$222.00	$222.00
Purchase #7	$98.87	5.597%	$104.4038	$104.40	$104.40	$104.40
7 purchase totals =	$1,223.02		$1,349.4402	$1,349.44	$1,349.40	$1,349.40