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	$71.34	12.780%	$80.4573	$80.46	$80.45	$80.50
Purchase #2	$204.59	9.808%	$224.6562	$224.66	$224.65	$224.70
Purchase #3	$12.84	8.179%	$13.8902	$13.89	$13.90	$13.90
Purchase #4	$25.97	6.219%	$27.5851	$27.59	$27.60	$27.60
Purchase #5	$213.92	4.443%	$223.4245	$223.42	$223.40	$223.40
Purchase #6	$170.75	10.812%	$189.2115	$189.21	$189.20	$189.20
Purchase #7	$98.36	13.208%	$111.3514	$111.35	$111.35	$111.40
7 purchase totals =	$797.77		$870.5762	$870.58	$870.55	$870.70