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	$109.69	10.461%	$121.1647	$121.16	$121.15	$121.20
Purchase #2	$154.58	6.801%	$165.093	$165.09	$165.10	$165.10
Purchase #3	$80.92	8.212%	$87.5652	$87.57	$87.55	$87.60
Purchase #4	$162.35	11.529%	$181.0673	$181.07	$181.05	$181.10
Purchase #5	$151.46	10.772%	$167.7753	$167.78	$167.80	$167.80
Purchase #6	$171.95	7.198%	$184.327	$184.33	$184.35	$184.30
Purchase #7	$102.78	9.854%	$112.9079	$112.91	$112.90	$112.90
7 purchase totals =	$933.73		$1,019.9004	$1,019.91	$1,019.90	$1,020.00