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	$21.58	10.295%	$23.8017	$23.80	$23.80	$23.80
Purchase #2	$157.88	8.871%	$171.8855	$171.89	$171.90	$171.90
Purchase #3	$46.37	11.511%	$51.7077	$51.71	$51.70	$51.70
Purchase #4	$98.27	13.568%	$111.6033	$111.60	$111.60	$111.60
Purchase #5	$85.36	3.367%	$88.2341	$88.23	$88.25	$88.20
Purchase #6	$85.52	12.742%	$96.417	$96.42	$96.40	$96.40
Purchase #7	$82.42	4.149%	$85.8396	$85.84	$85.85	$85.80
7 purchase totals =	$577.40		$629.4889	$629.49	$629.50	$629.40