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	$132.95	6.119%	$141.0852	$141.09	$141.10	$141.10
Purchase #2	$250.69	7.739%	$270.0909	$270.09	$270.10	$270.10
Purchase #3	$78.46	10.657%	$86.8215	$86.82	$86.80	$86.80
Purchase #4	$169.70	12.849%	$191.5048	$191.50	$191.50	$191.50
Purchase #5	$217.25	7.373%	$233.2678	$233.27	$233.25	$233.30
Purchase #6	$56.42	4.780%	$59.1169	$59.12	$59.10	$59.10
Purchase #7	$65.38	13.572%	$74.2534	$74.25	$74.25	$74.30
7 purchase totals =	$970.85		$1,056.1405	$1,056.14	$1,056.10	$1,056.20