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	$40.77	4.414%	$42.5696	$42.57	$42.55	$42.60
Purchase #2	$131.54	4.329%	$137.2344	$137.23	$137.25	$137.20
Purchase #3	$224.64	9.138%	$245.1676	$245.17	$245.15	$245.20
Purchase #4	$116.38	10.830%	$128.984	$128.98	$129.00	$129.00
Purchase #5	$10.43	4.185%	$10.8665	$10.87	$10.85	$10.90
Purchase #6	$205.70	8.307%	$222.7875	$222.79	$222.80	$222.80
Purchase #7	$229.46	7.334%	$246.2886	$246.29	$246.30	$246.30
7 purchase totals =	$958.92		$1,033.8982	$1,033.90	$1,033.90	$1,034.00