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	$240.94	4.555%	$251.9148	$251.91	$251.90	$251.90
Purchase #2	$81.42	12.441%	$91.5495	$91.55	$91.55	$91.50
Purchase #3	$51.39	6.603%	$54.7833	$54.78	$54.80	$54.80
Purchase #4	$226.48	12.502%	$254.7945	$254.79	$254.80	$254.80
Purchase #5	$185.77	5.872%	$196.6784	$196.68	$196.70	$196.70
Purchase #6	$204.82	8.182%	$221.5784	$221.58	$221.60	$221.60
Purchase #7	$187.90	11.242%	$209.0237	$209.02	$209.00	$209.00
7 purchase totals =	$1,178.72		$1,280.3226	$1,280.31	$1,280.35	$1,280.30