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	$135.39	10.447%	$149.5342	$149.53	$149.55	$149.50
Purchase #2	$100.52	11.528%	$112.1079	$112.11	$112.10	$112.10
Purchase #3	$90.53	12.241%	$101.6118	$101.61	$101.60	$101.60
Purchase #4	$160.28	5.400%	$168.9351	$168.94	$168.95	$168.90
Purchase #5	$71.38	9.328%	$78.0383	$78.04	$78.05	$78.00
Purchase #6	$188.60	3.299%	$194.8219	$194.82	$194.80	$194.80
Purchase #7	$28.54	8.602%	$30.995	$31.00	$31.00	$31.00
7 purchase totals =	$775.24		$836.0442	$836.05	$836.05	$835.90