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	$50.45	12.744%	$56.8793	$56.88	$56.90	$56.90
Purchase #2	$220.75	4.143%	$229.8957	$229.90	$229.90	$229.90
Purchase #3	$139.62	7.605%	$150.2381	$150.24	$150.25	$150.20
Purchase #4	$136.91	11.682%	$152.9038	$152.90	$152.90	$152.90
Purchase #5	$174.89	12.149%	$196.1374	$196.14	$196.15	$196.10
Purchase #6	$131.41	8.808%	$142.9846	$142.98	$143.00	$143.00
Purchase #7	$67.72	9.400%	$74.0857	$74.09	$74.10	$74.10
7 purchase totals =	$921.75		$1,003.1246	$1,003.13	$1,003.20	$1,003.10