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	$72.33	12.137%	$81.1087	$81.11	$81.10	$81.10
Purchase #2	$215.85	10.789%	$239.1381	$239.14	$239.15	$239.10
Purchase #3	$148.32	8.145%	$160.4007	$160.40	$160.40	$160.40
Purchase #4	$219.25	3.702%	$227.3666	$227.37	$227.35	$227.40
Purchase #5	$80.60	6.357%	$85.7237	$85.72	$85.70	$85.70
Purchase #6	$167.64	13.531%	$190.3234	$190.32	$190.30	$190.30
Purchase #7	$46.49	13.796%	$52.9038	$52.90	$52.90	$52.90
7 purchase totals =	$950.48		$1,036.9650	$1,036.96	$1,036.90	$1,036.90