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	$46.75	10.146%	$51.4933	$51.49	$51.50	$51.50
Purchase #2	$73.31	7.317%	$78.6741	$78.67	$78.65	$78.70
Purchase #3	$13.70	8.779%	$14.9027	$14.90	$14.90	$14.90
Purchase #4	$117.60	4.453%	$122.8367	$122.84	$122.85	$122.80
Purchase #5	$83.38	8.581%	$90.5348	$90.53	$90.55	$90.50
Purchase #6	$236.76	5.609%	$250.0399	$250.04	$250.05	$250.00
Purchase #7	$26.32	10.546%	$29.0957	$29.10	$29.10	$29.10
7 purchase totals =	$597.82		$637.5772	$637.57	$637.60	$637.50