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	$85.30	7.309%	$91.5346	$91.53	$91.55	$91.50
Purchase #2	$188.64	12.797%	$212.7803	$212.78	$212.80	$212.80
Purchase #3	$122.85	4.344%	$128.1866	$128.19	$128.20	$128.20
Purchase #4	$189.38	8.558%	$205.5871	$205.59	$205.60	$205.60
Purchase #5	$202.40	13.732%	$230.1936	$230.19	$230.20	$230.20
Purchase #6	$169.84	4.181%	$176.941	$176.94	$176.95	$176.90
Purchase #7	$19.61	9.663%	$21.5049	$21.50	$21.50	$21.50
7 purchase totals =	$978.02		$1,066.7281	$1,066.72	$1,066.80	$1,066.70