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	$35.66	5.136%	$37.4915	$37.49	$37.50	$37.50
Purchase #2	$13.57	6.179%	$14.4085	$14.41	$14.40	$14.40
Purchase #3	$244.76	3.739%	$253.9116	$253.91	$253.90	$253.90
Purchase #4	$87.88	11.585%	$98.0609	$98.06	$98.05	$98.10
Purchase #5	$154.62	10.732%	$171.2138	$171.21	$171.20	$171.20
Purchase #6	$171.65	12.337%	$192.8265	$192.83	$192.85	$192.80
Purchase #7	$64.27	10.527%	$71.0357	$71.04	$71.05	$71.00
7 purchase totals =	$772.41		$838.9485	$838.95	$838.95	$838.90