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	$90.78	9.725%	$99.6084	$99.61	$99.60	$99.60
Purchase #2	$249.31	9.696%	$273.4831	$273.48	$273.50	$273.50
Purchase #3	$155.92	9.384%	$170.5515	$170.55	$170.55	$170.60
Purchase #4	$32.75	5.224%	$34.4609	$34.46	$34.45	$34.50
Purchase #5	$210.62	12.441%	$236.8232	$236.82	$236.80	$236.80
Purchase #6	$185.58	13.399%	$210.4459	$210.45	$210.45	$210.40
Purchase #7	$45.70	11.229%	$50.8317	$50.83	$50.85	$50.80
7 purchase totals =	$970.66		$1,076.2047	$1,076.20	$1,076.20	$1,076.20