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	$107.72	3.721%	$111.7283	$111.73	$111.75	$111.70
Purchase #2	$46.45	6.782%	$49.6002	$49.60	$49.60	$49.60
Purchase #3	$231.78	7.354%	$248.8251	$248.83	$248.85	$248.80
Purchase #4	$7.88	3.256%	$8.1366	$8.14	$8.15	$8.10
Purchase #5	$245.41	10.359%	$270.832	$270.83	$270.85	$270.80
Purchase #6	$183.45	8.194%	$198.4819	$198.48	$198.50	$198.50
Purchase #7	$57.78	3.328%	$59.7029	$59.70	$59.70	$59.70
7 purchase totals =	$880.47		$947.3070	$947.31	$947.40	$947.20