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	$74.81	10.390%	$82.5828	$82.58	$82.60	$82.60
Purchase #2	$171.43	8.106%	$185.3261	$185.33	$185.35	$185.30
Purchase #3	$223.27	11.557%	$249.0733	$249.07	$249.05	$249.10
Purchase #4	$80.45	5.609%	$84.9624	$84.96	$84.95	$85.00
Purchase #5	$76.51	11.809%	$85.5451	$85.55	$85.55	$85.50
Purchase #6	$35.72	6.284%	$37.9646	$37.96	$37.95	$38.00
Purchase #7	$117.42	6.681%	$125.2648	$125.26	$125.25	$125.30
7 purchase totals =	$779.61		$850.7191	$850.71	$850.70	$850.80