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	$78.85	6.357%	$83.8625	$83.86	$83.85	$83.90
Purchase #2	$41.84	9.221%	$45.6981	$45.70	$45.70	$45.70
Purchase #3	$90.55	12.502%	$101.8706	$101.87	$101.85	$101.90
Purchase #4	$50.87	4.311%	$53.063	$53.06	$53.05	$53.10
Purchase #5	$53.45	5.814%	$56.5576	$56.56	$56.55	$56.60
Purchase #6	$68.88	6.559%	$73.3978	$73.40	$73.40	$73.40
Purchase #7	$163.95	4.597%	$171.4868	$171.49	$171.50	$171.50
7 purchase totals =	$548.39		$585.9364	$585.94	$585.90	$586.10