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	$246.73	13.606%	$280.3001	$280.30	$280.30	$280.30
Purchase #2	$108.73	12.666%	$122.5017	$122.50	$122.50	$122.50
Purchase #3	$250.51	12.386%	$281.5382	$281.54	$281.55	$281.50
Purchase #4	$49.32	5.378%	$51.9724	$51.97	$51.95	$52.00
Purchase #5	$162.64	13.786%	$185.0616	$185.06	$185.05	$185.10
Purchase #6	$164.33	4.354%	$171.4849	$171.48	$171.50	$171.50
Purchase #7	$188.76	13.320%	$213.9028	$213.90	$213.90	$213.90
7 purchase totals =	$1,171.02		$1,306.7617	$1,306.75	$1,306.75	$1,306.80