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	$102.69	9.614%	$112.5626	$112.56	$112.55	$112.60
Purchase #2	$79.25	12.552%	$89.1975	$89.20	$89.20	$89.20
Purchase #3	$145.92	6.111%	$154.8372	$154.84	$154.85	$154.80
Purchase #4	$101.66	5.154%	$106.8996	$106.90	$106.90	$106.90
Purchase #5	$43.70	10.778%	$48.41	$48.41	$48.40	$48.40
Purchase #6	$109.51	13.618%	$124.4231	$124.42	$124.40	$124.40
Purchase #7	$133.54	12.850%	$150.6999	$150.70	$150.70	$150.70
7 purchase totals =	$716.27		$787.0299	$787.03	$787.00	$787.00