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	$208.61	9.483%	$228.3925	$228.39	$228.40	$228.40
Purchase #2	$96.99	5.469%	$102.2944	$102.29	$102.30	$102.30
Purchase #3	$84.72	6.276%	$90.037	$90.04	$90.05	$90.00
Purchase #4	$150.83	6.325%	$160.37	$160.37	$160.35	$160.40
Purchase #5	$119.89	9.464%	$131.2364	$131.24	$131.25	$131.20
Purchase #6	$182.35	6.462%	$194.1335	$194.13	$194.15	$194.10
Purchase #7	$6.92	4.782%	$7.2509	$7.25	$7.25	$7.30
7 purchase totals =	$850.31		$913.7147	$913.71	$913.75	$913.70