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	$104.77	4.225%	$109.1965	$109.20	$109.20	$109.20
Purchase #2	$234.84	10.262%	$258.9393	$258.94	$258.95	$258.90
Purchase #3	$175.79	13.539%	$199.5902	$199.59	$199.60	$199.60
Purchase #4	$198.90	13.838%	$226.4238	$226.42	$226.40	$226.40
Purchase #5	$118.25	4.320%	$123.3584	$123.36	$123.35	$123.40
Purchase #6	$33.59	4.432%	$35.0787	$35.08	$35.10	$35.10
Purchase #7	$164.27	10.362%	$181.2917	$181.29	$181.30	$181.30
7 purchase totals =	$1,030.41		$1,133.8786	$1,133.88	$1,133.90	$1,133.90