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	$11.89	13.841%	$13.5357	$13.54	$13.55	$13.50
Purchase #2	$242.94	8.398%	$263.3421	$263.34	$263.35	$263.30
Purchase #3	$109.50	13.205%	$123.9595	$123.96	$123.95	$124.00
Purchase #4	$175.49	4.445%	$183.2905	$183.29	$183.30	$183.30
Purchase #5	$74.59	11.166%	$82.9187	$82.92	$82.90	$82.90
Purchase #6	$221.29	5.742%	$233.9965	$234.00	$234.00	$234.00
Purchase #7	$194.42	11.314%	$216.4167	$216.42	$216.40	$216.40
7 purchase totals =	$1,030.12		$1,117.4597	$1,117.47	$1,117.45	$1,117.40