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	$111.33	8.134%	$120.3856	$120.39	$120.40	$120.40
Purchase #2	$151.76	3.167%	$156.5662	$156.57	$156.55	$156.60
Purchase #3	$224.51	13.860%	$255.6271	$255.63	$255.65	$255.60
Purchase #4	$193.35	5.112%	$203.2341	$203.23	$203.25	$203.20
Purchase #5	$168.71	9.669%	$185.0226	$185.02	$185.00	$185.00
Purchase #6	$98.82	7.605%	$106.3353	$106.34	$106.35	$106.30
Purchase #7	$165.35	10.305%	$182.3893	$182.39	$182.40	$182.40
7 purchase totals =	$1,113.83		$1,209.5602	$1,209.57	$1,209.60	$1,209.50