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	$127.41	3.218%	$131.5101	$131.51	$131.50	$131.50
Purchase #2	$143.59	3.288%	$148.3112	$148.31	$148.30	$148.30
Purchase #3	$196.85	3.283%	$203.3126	$203.31	$203.30	$203.30
Purchase #4	$139.41	7.827%	$150.3216	$150.32	$150.30	$150.30
Purchase #5	$30.28	13.538%	$34.3793	$34.38	$34.40	$34.40
Purchase #6	$67.98	4.801%	$71.2437	$71.24	$71.25	$71.20
Purchase #7	$239.59	8.195%	$259.2244	$259.22	$259.20	$259.20
7 purchase totals =	$945.11		$998.3029	$998.29	$998.25	$998.20