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	$95.82	3.492%	$99.166	$99.17	$99.15	$99.20
Purchase #2	$242.97	9.407%	$265.8262	$265.83	$265.85	$265.80
Purchase #3	$169.29	13.858%	$192.7502	$192.75	$192.75	$192.80
Purchase #4	$93.82	7.196%	$100.5713	$100.57	$100.55	$100.60
Purchase #5	$79.57	7.528%	$85.56	$85.56	$85.55	$85.60
Purchase #6	$142.62	11.394%	$158.8701	$158.87	$158.85	$158.90
Purchase #7	$218.48	4.297%	$227.8681	$227.87	$227.85	$227.90
7 purchase totals =	$1,042.57		$1,130.6119	$1,130.62	$1,130.55	$1,130.80