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	$223.71	11.496%	$249.4277	$249.43	$249.45	$249.40
Purchase #2	$75.41	3.607%	$78.13	$78.13	$78.15	$78.10
Purchase #3	$225.90	5.718%	$238.817	$238.82	$238.80	$238.80
Purchase #4	$110.31	8.187%	$119.3411	$119.34	$119.35	$119.30
Purchase #5	$90.43	13.127%	$102.3007	$102.30	$102.30	$102.30
Purchase #6	$21.54	10.777%	$23.8614	$23.86	$23.85	$23.90
Purchase #7	$119.70	4.113%	$124.6233	$124.62	$124.60	$124.60
7 purchase totals =	$867.00		$936.5012	$936.50	$936.50	$936.40