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	$80.75	12.556%	$90.889	$90.89	$90.90	$90.90
Purchase #2	$92.41	10.702%	$102.2997	$102.30	$102.30	$102.30
Purchase #3	$172.37	3.459%	$178.3323	$178.33	$178.35	$178.30
Purchase #4	$74.69	5.194%	$78.5694	$78.57	$78.55	$78.60
Purchase #5	$167.34	13.366%	$189.7067	$189.71	$189.70	$189.70
Purchase #6	$31.86	5.531%	$33.6222	$33.62	$33.60	$33.60
Purchase #7	$248.35	7.532%	$267.0557	$267.06	$267.05	$267.10
7 purchase totals =	$867.77		$940.4750	$940.48	$940.45	$940.50