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	$38.50	4.274%	$40.1455	$40.15	$40.15	$40.10
Purchase #2	$48.87	3.236%	$50.4514	$50.45	$50.45	$50.50
Purchase #3	$48.71	12.458%	$54.7783	$54.78	$54.80	$54.80
Purchase #4	$211.75	13.708%	$240.7767	$240.78	$240.80	$240.80
Purchase #5	$105.26	7.508%	$113.1629	$113.16	$113.15	$113.20
Purchase #6	$31.94	10.859%	$35.4084	$35.41	$35.40	$35.40
Purchase #7	$73.28	9.377%	$80.1515	$80.15	$80.15	$80.20
7 purchase totals =	$558.31		$614.8747	$614.88	$614.90	$615.00