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	$188.91	5.610%	$199.5079	$199.51	$199.50	$199.50
Purchase #2	$153.46	13.328%	$173.9131	$173.91	$173.90	$173.90
Purchase #3	$154.72	3.355%	$159.9109	$159.91	$159.90	$159.90
Purchase #4	$66.82	13.533%	$75.8628	$75.86	$75.85	$75.90
Purchase #5	$70.59	12.214%	$79.2119	$79.21	$79.20	$79.20
Purchase #6	$27.57	13.583%	$31.3148	$31.31	$31.30	$31.30
Purchase #7	$107.79	11.225%	$119.8894	$119.89	$119.90	$119.90
7 purchase totals =	$769.86		$839.6108	$839.60	$839.55	$839.60