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	$10.29	9.265%	$11.2434	$11.24	$11.25	$11.20
Purchase #2	$123.54	13.352%	$140.0351	$140.04	$140.05	$140.00
Purchase #3	$237.96	5.259%	$250.4743	$250.47	$250.45	$250.50
Purchase #4	$177.69	4.711%	$186.061	$186.06	$186.05	$186.10
Purchase #5	$10.74	10.685%	$11.8876	$11.89	$11.90	$11.90
Purchase #6	$154.60	9.601%	$169.4431	$169.44	$169.45	$169.40
Purchase #7	$28.66	9.577%	$31.4048	$31.40	$31.40	$31.40
7 purchase totals =	$743.48		$800.5493	$800.54	$800.55	$800.50