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	$52.69	8.234%	$57.0285	$57.03	$57.05	$57.00
Purchase #2	$169.72	9.544%	$185.9181	$185.92	$185.90	$185.90
Purchase #3	$38.87	3.140%	$40.0905	$40.09	$40.10	$40.10
Purchase #4	$31.35	9.254%	$34.2511	$34.25	$34.25	$34.30
Purchase #5	$226.95	7.408%	$243.7625	$243.76	$243.75	$243.80
Purchase #6	$178.65	9.772%	$196.1077	$196.11	$196.10	$196.10
Purchase #7	$248.82	13.226%	$281.7289	$281.73	$281.75	$281.70
7 purchase totals =	$947.05		$1,038.8873	$1,038.89	$1,038.90	$1,038.90