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	$234.79	6.482%	$250.0091	$250.01	$250.00	$250.00
Purchase #2	$68.81	13.782%	$78.2934	$78.29	$78.30	$78.30
Purchase #3	$238.44	13.256%	$270.0476	$270.05	$270.05	$270.00
Purchase #4	$244.64	4.747%	$256.2531	$256.25	$256.25	$256.30
Purchase #5	$42.55	6.839%	$45.46	$45.46	$45.45	$45.50
Purchase #6	$243.45	9.703%	$267.072	$267.07	$267.05	$267.10
Purchase #7	$71.96	3.779%	$74.6794	$74.68	$74.70	$74.70
7 purchase totals =	$1,144.64		$1,241.8146	$1,241.81	$1,241.80	$1,241.90