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	$38.35	5.134%	$40.3189	$40.32	$40.30	$40.30
Purchase #2	$24.28	12.394%	$27.2893	$27.29	$27.30	$27.30
Purchase #3	$196.28	13.137%	$222.0653	$222.07	$222.05	$222.10
Purchase #4	$142.59	11.575%	$159.0948	$159.09	$159.10	$159.10
Purchase #5	$48.63	8.867%	$52.942	$52.94	$52.95	$52.90
Purchase #6	$211.90	10.112%	$233.3273	$233.33	$233.35	$233.30
Purchase #7	$64.68	11.327%	$72.0063	$72.01	$72.00	$72.00
7 purchase totals =	$726.71		$807.0439	$807.05	$807.05	$807.00