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	$12.39	11.442%	$13.8077	$13.81	$13.80	$13.80
Purchase #2	$169.55	12.327%	$190.4504	$190.45	$190.45	$190.50
Purchase #3	$146.36	3.491%	$151.4694	$151.47	$151.45	$151.50
Purchase #4	$102.73	12.365%	$115.4326	$115.43	$115.45	$115.40
Purchase #5	$160.45	11.769%	$179.3334	$179.33	$179.35	$179.30
Purchase #6	$128.56	3.758%	$133.3913	$133.39	$133.40	$133.40
Purchase #7	$71.30	10.631%	$78.8799	$78.88	$78.90	$78.90
7 purchase totals =	$791.34		$862.7647	$862.76	$862.80	$862.80