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	$235.28	3.416%	$243.3172	$243.32	$243.30	$243.30
Purchase #2	$55.89	6.665%	$59.6151	$59.62	$59.60	$59.60
Purchase #3	$186.60	3.413%	$192.9687	$192.97	$192.95	$193.00
Purchase #4	$99.52	9.654%	$109.1277	$109.13	$109.15	$109.10
Purchase #5	$101.90	11.671%	$113.7927	$113.79	$113.80	$113.80
Purchase #6	$13.88	4.321%	$14.4798	$14.48	$14.50	$14.50
Purchase #7	$21.60	9.369%	$23.6237	$23.62	$23.60	$23.60
7 purchase totals =	$714.67		$756.9249	$756.93	$756.90	$756.90