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	$139.86	9.810%	$153.5803	$153.58	$153.60	$153.60
Purchase #2	$44.84	12.865%	$50.6087	$50.61	$50.60	$50.60
Purchase #3	$45.48	6.285%	$48.3384	$48.34	$48.35	$48.30
Purchase #4	$92.85	7.545%	$99.8555	$99.86	$99.85	$99.90
Purchase #5	$76.72	10.560%	$84.8216	$84.82	$84.80	$84.80
Purchase #6	$133.37	11.396%	$148.5688	$148.57	$148.55	$148.60
Purchase #7	$240.53	13.724%	$273.5403	$273.54	$273.55	$273.50
7 purchase totals =	$773.65		$859.3136	$859.32	$859.30	$859.30