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	$242.41	3.472%	$250.8265	$250.83	$250.85	$250.80
Purchase #2	$174.52	8.766%	$189.8184	$189.82	$189.80	$189.80
Purchase #3	$206.88	7.798%	$223.0125	$223.01	$223.00	$223.00
Purchase #4	$81.37	11.714%	$90.9017	$90.90	$90.90	$90.90
Purchase #5	$168.45	11.367%	$187.5977	$187.60	$187.60	$187.60
Purchase #6	$143.41	9.425%	$156.9264	$156.93	$156.95	$156.90
Purchase #7	$76.60	8.508%	$83.1171	$83.12	$83.10	$83.10
7 purchase totals =	$1,093.64		$1,182.2003	$1,182.21	$1,182.20	$1,182.10