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	$148.25	5.547%	$156.4734	$156.47	$156.45	$156.50
Purchase #2	$136.42	5.451%	$143.8563	$143.86	$143.85	$143.90
Purchase #3	$215.62	12.728%	$243.0641	$243.06	$243.05	$243.10
Purchase #4	$106.81	7.102%	$114.3956	$114.40	$114.40	$114.40
Purchase #5	$225.69	13.667%	$256.5351	$256.54	$256.55	$256.50
Purchase #6	$115.92	10.624%	$128.2353	$128.24	$128.25	$128.20
Purchase #7	$234.88	6.139%	$249.2993	$249.30	$249.30	$249.30
7 purchase totals =	$1,183.59		$1,291.8591	$1,291.87	$1,291.85	$1,291.90