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	$78.96	5.678%	$83.4433	$83.44	$83.45	$83.40
Purchase #2	$38.96	8.747%	$42.3678	$42.37	$42.35	$42.40
Purchase #3	$193.31	12.197%	$216.888	$216.89	$216.90	$216.90
Purchase #4	$115.67	10.841%	$128.2098	$128.21	$128.20	$128.20
Purchase #5	$170.56	4.416%	$178.0919	$178.09	$178.10	$178.10
Purchase #6	$205.90	8.710%	$223.8339	$223.83	$223.85	$223.80
Purchase #7	$65.55	10.501%	$72.4334	$72.43	$72.45	$72.40
7 purchase totals =	$868.91		$945.2681	$945.26	$945.30	$945.20