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	$46.44	10.695%	$51.4068	$51.41	$51.40	$51.40
Purchase #2	$199.49	12.660%	$224.7454	$224.75	$224.75	$224.70
Purchase #3	$35.52	9.559%	$38.9154	$38.92	$38.90	$38.90
Purchase #4	$124.36	10.618%	$137.5645	$137.56	$137.55	$137.60
Purchase #5	$83.78	10.827%	$92.8509	$92.85	$92.85	$92.90
Purchase #6	$121.93	4.520%	$127.4412	$127.44	$127.45	$127.40
Purchase #7	$28.56	10.626%	$31.5948	$31.59	$31.60	$31.60
7 purchase totals =	$640.08		$704.5190	$704.52	$704.50	$704.50