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	$237.31	9.278%	$259.3276	$259.33	$259.35	$259.30
Purchase #2	$230.65	6.327%	$245.2432	$245.24	$245.25	$245.20
Purchase #3	$231.86	3.299%	$239.5091	$239.51	$239.50	$239.50
Purchase #4	$6.31	12.473%	$7.097	$7.10	$7.10	$7.10
Purchase #5	$100.31	9.119%	$109.4573	$109.46	$109.45	$109.50
Purchase #6	$188.34	13.640%	$214.0296	$214.03	$214.05	$214.00
Purchase #7	$160.92	12.661%	$181.2941	$181.29	$181.30	$181.30
7 purchase totals =	$1,155.70		$1,255.9579	$1,255.96	$1,256.00	$1,255.90