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	$99.27	11.247%	$110.4349	$110.43	$110.45	$110.40
Purchase #2	$186.47	7.580%	$200.6044	$200.60	$200.60	$200.60
Purchase #3	$177.69	3.591%	$184.0708	$184.07	$184.05	$184.10
Purchase #4	$11.91	7.249%	$12.7734	$12.77	$12.75	$12.80
Purchase #5	$78.88	11.732%	$88.1342	$88.13	$88.15	$88.10
Purchase #6	$136.46	4.314%	$142.3469	$142.35	$142.35	$142.30
Purchase #7	$116.86	3.159%	$120.5516	$120.55	$120.55	$120.60
7 purchase totals =	$807.54		$858.9162	$858.90	$858.90	$858.90