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	$200.37	6.570%	$213.5343	$213.53	$213.55	$213.50
Purchase #2	$179.47	12.766%	$202.3811	$202.38	$202.40	$202.40
Purchase #3	$150.39	8.106%	$162.5806	$162.58	$162.60	$162.60
Purchase #4	$79.73	13.102%	$90.1762	$90.18	$90.20	$90.20
Purchase #5	$80.93	12.585%	$91.115	$91.12	$91.10	$91.10
Purchase #6	$205.88	9.459%	$225.3542	$225.35	$225.35	$225.40
Purchase #7	$82.34	10.276%	$90.8013	$90.80	$90.80	$90.80
7 purchase totals =	$979.11		$1,075.9427	$1,075.94	$1,076.00	$1,076.00