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	$100.99	11.389%	$112.4918	$112.49	$112.50	$112.50
Purchase #2	$122.37	7.519%	$131.571	$131.57	$131.55	$131.60
Purchase #3	$41.45	5.714%	$43.8185	$43.82	$43.80	$43.80
Purchase #4	$202.48	3.482%	$209.5304	$209.53	$209.55	$209.50
Purchase #5	$237.45	5.605%	$250.7591	$250.76	$250.75	$250.80
Purchase #6	$217.96	13.277%	$246.8985	$246.90	$246.90	$246.90
Purchase #7	$17.31	4.582%	$18.1031	$18.10	$18.10	$18.10
7 purchase totals =	$940.01		$1,013.1724	$1,013.17	$1,013.15	$1,013.20