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	$95.51	11.262%	$106.2663	$106.27	$106.25	$106.30
Purchase #2	$53.77	11.142%	$59.7611	$59.76	$59.75	$59.80
Purchase #3	$222.56	6.870%	$237.8499	$237.85	$237.85	$237.80
Purchase #4	$184.38	5.239%	$194.0397	$194.04	$194.05	$194.00
Purchase #5	$131.54	7.130%	$140.9188	$140.92	$140.90	$140.90
Purchase #6	$231.87	3.838%	$240.7692	$240.77	$240.75	$240.80
Purchase #7	$248.69	12.850%	$280.6467	$280.65	$280.65	$280.60
7 purchase totals =	$1,168.32		$1,260.2517	$1,260.26	$1,260.20	$1,260.20