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	$202.39	9.310%	$221.2325	$221.23	$221.25	$221.20
Purchase #2	$145.85	3.126%	$150.4093	$150.41	$150.40	$150.40
Purchase #3	$151.52	3.531%	$156.8702	$156.87	$156.85	$156.90
Purchase #4	$241.43	3.688%	$250.3339	$250.33	$250.35	$250.30
Purchase #5	$194.48	13.702%	$221.1276	$221.13	$221.15	$221.10
Purchase #6	$134.47	8.762%	$146.2523	$146.25	$146.25	$146.30
Purchase #7	$117.31	11.834%	$131.1925	$131.19	$131.20	$131.20
7 purchase totals =	$1,187.45		$1,277.4183	$1,277.41	$1,277.45	$1,277.40