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	$237.91	9.780%	$261.1776	$261.18	$261.20	$261.20
Purchase #2	$216.95	9.772%	$238.1504	$238.15	$238.15	$238.20
Purchase #3	$33.44	9.322%	$36.5573	$36.56	$36.55	$36.60
Purchase #4	$146.51	11.180%	$162.8898	$162.89	$162.90	$162.90
Purchase #5	$52.83	13.144%	$59.774	$59.77	$59.75	$59.80
Purchase #6	$48.42	5.609%	$51.1359	$51.14	$51.15	$51.10
Purchase #7	$22.44	7.796%	$24.1894	$24.19	$24.20	$24.20
7 purchase totals =	$758.50		$833.8744	$833.88	$833.90	$834.00