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	$38.59	6.612%	$41.1416	$41.14	$41.15	$41.10
Purchase #2	$54.86	8.445%	$59.4929	$59.49	$59.50	$59.50
Purchase #3	$109.32	9.357%	$119.5491	$119.55	$119.55	$119.50
Purchase #4	$62.29	5.247%	$65.5584	$65.56	$65.55	$65.60
Purchase #5	$143.36	13.163%	$162.2305	$162.23	$162.25	$162.20
Purchase #6	$110.42	10.770%	$122.3122	$122.31	$122.30	$122.30
Purchase #7	$180.55	12.557%	$203.2217	$203.22	$203.20	$203.20
7 purchase totals =	$699.39		$773.5064	$773.50	$773.50	$773.40