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	$150.85	5.318%	$158.8722	$158.87	$158.85	$158.90
Purchase #2	$121.95	7.544%	$131.1499	$131.15	$131.15	$131.10
Purchase #3	$39.54	6.765%	$42.2149	$42.21	$42.20	$42.20
Purchase #4	$27.36	12.288%	$30.722	$30.72	$30.70	$30.70
Purchase #5	$49.77	13.385%	$56.4317	$56.43	$56.45	$56.40
Purchase #6	$209.47	9.530%	$229.4325	$229.43	$229.45	$229.40
Purchase #7	$186.45	10.426%	$205.8893	$205.89	$205.90	$205.90
7 purchase totals =	$785.39		$854.7125	$854.70	$854.70	$854.60