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	$245.69	10.166%	$270.6668	$270.67	$270.65	$270.70
Purchase #2	$108.74	3.769%	$112.8384	$112.84	$112.85	$112.80
Purchase #3	$152.90	3.361%	$158.039	$158.04	$158.05	$158.00
Purchase #4	$195.45	13.506%	$221.8475	$221.85	$221.85	$221.80
Purchase #5	$78.78	12.403%	$88.5511	$88.55	$88.55	$88.60
Purchase #6	$107.35	10.459%	$118.5777	$118.58	$118.60	$118.60
Purchase #7	$194.39	3.201%	$200.6124	$200.61	$200.60	$200.60
7 purchase totals =	$1,083.30		$1,171.1329	$1,171.14	$1,171.15	$1,171.10