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	$241.38	6.493%	$257.0528	$257.05	$257.05	$257.10
Purchase #2	$228.31	12.551%	$256.9652	$256.97	$256.95	$257.00
Purchase #3	$62.93	12.649%	$70.89	$70.89	$70.90	$70.90
Purchase #4	$245.58	4.208%	$255.914	$255.91	$255.90	$255.90
Purchase #5	$99.37	6.395%	$105.7247	$105.72	$105.70	$105.70
Purchase #6	$168.39	13.605%	$191.2995	$191.30	$191.30	$191.30
Purchase #7	$99.38	5.558%	$104.9035	$104.90	$104.90	$104.90
7 purchase totals =	$1,145.34		$1,242.7497	$1,242.74	$1,242.70	$1,242.80