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	$90.80	8.807%	$98.7968	$98.80	$98.80	$98.80
Purchase #2	$114.64	7.479%	$123.2139	$123.21	$123.20	$123.20
Purchase #3	$90.88	9.578%	$99.5845	$99.58	$99.60	$99.60
Purchase #4	$85.43	12.449%	$96.0652	$96.07	$96.05	$96.10
Purchase #5	$43.57	6.754%	$46.5127	$46.51	$46.50	$46.50
Purchase #6	$210.54	9.632%	$230.8192	$230.82	$230.80	$230.80
Purchase #7	$146.82	9.507%	$160.7782	$160.78	$160.80	$160.80
7 purchase totals =	$782.68		$855.7705	$855.77	$855.75	$855.80