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	$132.72	13.641%	$150.8243	$150.82	$150.80	$150.80
Purchase #2	$40.48	13.161%	$45.8076	$45.81	$45.80	$45.80
Purchase #3	$36.44	10.658%	$40.3238	$40.32	$40.30	$40.30
Purchase #4	$120.60	6.584%	$128.5403	$128.54	$128.55	$128.50
Purchase #5	$88.86	11.210%	$98.8212	$98.82	$98.80	$98.80
Purchase #6	$175.62	6.124%	$186.375	$186.38	$186.40	$186.40
Purchase #7	$17.45	8.141%	$18.8706	$18.87	$18.85	$18.90
7 purchase totals =	$612.17		$669.5628	$669.56	$669.50	$669.50