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	$48.31	12.345%	$54.2739	$54.27	$54.25	$54.30
Purchase #2	$246.78	9.596%	$270.461	$270.46	$270.45	$270.50
Purchase #3	$55.94	4.423%	$58.4142	$58.41	$58.40	$58.40
Purchase #4	$104.27	7.853%	$112.4583	$112.46	$112.45	$112.50
Purchase #5	$121.45	4.204%	$126.5558	$126.56	$126.55	$126.60
Purchase #6	$5.89	4.645%	$6.1636	$6.16	$6.15	$6.20
Purchase #7	$52.85	6.242%	$56.1489	$56.15	$56.15	$56.10
7 purchase totals =	$635.49		$684.4757	$684.47	$684.40	$684.60