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	$96.31	8.233%	$104.2392	$104.24	$104.25	$104.20
Purchase #2	$80.94	8.828%	$88.0854	$88.09	$88.10	$88.10
Purchase #3	$67.66	13.674%	$76.9118	$76.91	$76.90	$76.90
Purchase #4	$136.91	9.560%	$149.9986	$150.00	$150.00	$150.00
Purchase #5	$81.60	5.226%	$85.8644	$85.86	$85.85	$85.90
Purchase #6	$114.48	3.524%	$118.5143	$118.51	$118.50	$118.50
Purchase #7	$40.40	5.402%	$42.5824	$42.58	$42.60	$42.60
7 purchase totals =	$618.30		$666.1961	$666.19	$666.20	$666.20