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	$246.65	9.808%	$270.8414	$270.84	$270.85	$270.80
Purchase #2	$216.58	10.124%	$238.5066	$238.51	$238.50	$238.50
Purchase #3	$85.93	5.839%	$90.9475	$90.95	$90.95	$90.90
Purchase #4	$85.65	6.686%	$91.3766	$91.38	$91.40	$91.40
Purchase #5	$237.29	12.352%	$266.6001	$266.60	$266.60	$266.60
Purchase #6	$76.42	13.616%	$86.8253	$86.83	$86.85	$86.80
Purchase #7	$12.74	3.571%	$13.1949	$13.19	$13.20	$13.20
7 purchase totals =	$961.26		$1,058.2924	$1,058.30	$1,058.35	$1,058.20