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	$147.67	11.334%	$164.4069	$164.41	$164.40	$164.40
Purchase #2	$231.85	8.209%	$250.8826	$250.88	$250.90	$250.90
Purchase #3	$104.54	13.695%	$118.8568	$118.86	$118.85	$118.90
Purchase #4	$159.28	5.714%	$168.3813	$168.38	$168.40	$168.40
Purchase #5	$244.76	3.591%	$253.5493	$253.55	$253.55	$253.50
Purchase #6	$234.35	5.632%	$247.5486	$247.55	$247.55	$247.50
Purchase #7	$108.59	7.161%	$116.3661	$116.37	$116.35	$116.40
7 purchase totals =	$1,231.04		$1,319.9916	$1,320.00	$1,320.00	$1,320.00