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	$141.79	6.628%	$151.1878	$151.19	$151.20	$151.20
Purchase #2	$73.71	12.128%	$82.6495	$82.65	$82.65	$82.60
Purchase #3	$194.53	11.858%	$217.5974	$217.60	$217.60	$217.60
Purchase #4	$185.29	4.590%	$193.7948	$193.79	$193.80	$193.80
Purchase #5	$46.88	13.613%	$53.2618	$53.26	$53.25	$53.30
Purchase #6	$84.82	5.133%	$89.1738	$89.17	$89.15	$89.20
Purchase #7	$49.46	5.150%	$52.0072	$52.01	$52.00	$52.00
7 purchase totals =	$776.48		$839.6723	$839.67	$839.65	$839.70