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	$171.32	12.587%	$192.884	$192.88	$192.90	$192.90
Purchase #2	$193.84	3.342%	$200.3181	$200.32	$200.30	$200.30
Purchase #3	$30.44	10.430%	$33.6149	$33.61	$33.60	$33.60
Purchase #4	$38.41	5.407%	$40.4868	$40.49	$40.50	$40.50
Purchase #5	$198.71	5.626%	$209.8894	$209.89	$209.90	$209.90
Purchase #6	$12.55	9.185%	$13.7027	$13.70	$13.70	$13.70
Purchase #7	$145.59	10.218%	$160.4664	$160.47	$160.45	$160.50
7 purchase totals =	$790.86		$851.3623	$851.36	$851.35	$851.40