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	$228.45	8.739%	$248.4142	$248.41	$248.40	$248.40
Purchase #2	$166.35	8.345%	$180.2319	$180.23	$180.25	$180.20
Purchase #3	$228.93	5.783%	$242.169	$242.17	$242.15	$242.20
Purchase #4	$131.76	10.723%	$145.8886	$145.89	$145.90	$145.90
Purchase #5	$37.59	9.248%	$41.0663	$41.07	$41.05	$41.10
Purchase #6	$188.50	11.531%	$210.2359	$210.24	$210.25	$210.20
Purchase #7	$206.90	12.538%	$232.8411	$232.84	$232.85	$232.80
7 purchase totals =	$1,188.48		$1,300.8470	$1,300.85	$1,300.85	$1,300.80