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	$35.84	13.114%	$40.5401	$40.54	$40.55	$40.50
Purchase #2	$223.38	6.373%	$237.616	$237.62	$237.60	$237.60
Purchase #3	$56.60	5.828%	$59.8986	$59.90	$59.90	$59.90
Purchase #4	$229.38	7.773%	$247.2097	$247.21	$247.20	$247.20
Purchase #5	$235.29	5.765%	$248.8545	$248.85	$248.85	$248.90
Purchase #6	$175.89	6.392%	$187.1329	$187.13	$187.15	$187.10
Purchase #7	$174.50	7.221%	$187.1006	$187.10	$187.10	$187.10
7 purchase totals =	$1,130.88		$1,208.3524	$1,208.35	$1,208.35	$1,208.30