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	$69.27	8.422%	$75.1039	$75.10	$75.10	$75.10
Purchase #2	$94.88	6.220%	$100.7815	$100.78	$100.80	$100.80
Purchase #3	$137.41	4.867%	$144.0977	$144.10	$144.10	$144.10
Purchase #4	$35.32	13.387%	$40.0483	$40.05	$40.05	$40.00
Purchase #5	$97.93	11.859%	$109.5435	$109.54	$109.55	$109.50
Purchase #6	$241.46	9.361%	$264.0631	$264.06	$264.05	$264.10
Purchase #7	$76.75	5.465%	$80.9444	$80.94	$80.95	$80.90
7 purchase totals =	$753.02		$814.5824	$814.57	$814.60	$814.50