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	$215.57	10.656%	$238.5411	$238.54	$238.55	$238.50
Purchase #2	$161.61	3.469%	$167.2163	$167.22	$167.20	$167.20
Purchase #3	$133.65	5.839%	$141.4538	$141.45	$141.45	$141.50
Purchase #4	$37.72	11.652%	$42.1151	$42.12	$42.10	$42.10
Purchase #5	$54.86	7.671%	$59.0683	$59.07	$59.05	$59.10
Purchase #6	$219.50	4.313%	$228.967	$228.97	$228.95	$229.00
Purchase #7	$110.54	9.361%	$120.8876	$120.89	$120.90	$120.90
7 purchase totals =	$933.45		$998.2492	$998.26	$998.20	$998.30