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	$134.49	10.213%	$148.2255	$148.23	$148.25	$148.20
Purchase #2	$177.84	8.409%	$192.7946	$192.79	$192.80	$192.80
Purchase #3	$131.58	6.354%	$139.9406	$139.94	$139.95	$139.90
Purchase #4	$225.89	3.869%	$234.6297	$234.63	$234.65	$234.60
Purchase #5	$80.92	10.628%	$89.5202	$89.52	$89.50	$89.50
Purchase #6	$58.92	10.744%	$65.2504	$65.25	$65.25	$65.30
Purchase #7	$198.82	5.683%	$210.1189	$210.12	$210.10	$210.10
7 purchase totals =	$1,008.46		$1,080.4799	$1,080.48	$1,080.50	$1,080.40