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	$110.77	3.709%	$114.8785	$114.88	$114.90	$114.90
Purchase #2	$245.95	13.118%	$278.2137	$278.21	$278.20	$278.20
Purchase #3	$133.84	12.449%	$150.5017	$150.50	$150.50	$150.50
Purchase #4	$139.53	10.786%	$154.5797	$154.58	$154.60	$154.60
Purchase #5	$65.38	3.270%	$67.5179	$67.52	$67.50	$67.50
Purchase #6	$100.93	4.398%	$105.3689	$105.37	$105.35	$105.40
Purchase #7	$94.61	13.675%	$107.5479	$107.55	$107.55	$107.50
7 purchase totals =	$891.01		$978.6083	$978.61	$978.60	$978.60