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	$122.53	4.272%	$127.7645	$127.76	$127.75	$127.80
Purchase #2	$166.50	3.360%	$172.0944	$172.09	$172.10	$172.10
Purchase #3	$128.76	6.309%	$136.8835	$136.88	$136.90	$136.90
Purchase #4	$162.25	3.418%	$167.7957	$167.80	$167.80	$167.80
Purchase #5	$220.59	4.124%	$229.6871	$229.69	$229.70	$229.70
Purchase #6	$13.57	8.471%	$14.7195	$14.72	$14.70	$14.70
Purchase #7	$10.64	5.319%	$11.2059	$11.21	$11.20	$11.20
7 purchase totals =	$824.84		$860.1506	$860.15	$860.15	$860.20