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	$249.85	5.433%	$263.4244	$263.42	$263.40	$263.40
Purchase #2	$174.38	3.865%	$181.1198	$181.12	$181.10	$181.10
Purchase #3	$83.41	13.770%	$94.8956	$94.90	$94.90	$94.90
Purchase #4	$30.67	6.254%	$32.5881	$32.59	$32.60	$32.60
Purchase #5	$140.74	11.412%	$156.8012	$156.80	$156.80	$156.80
Purchase #6	$242.64	8.533%	$263.3445	$263.34	$263.35	$263.30
Purchase #7	$132.52	11.238%	$147.4126	$147.41	$147.40	$147.40
7 purchase totals =	$1,054.21		$1,139.5862	$1,139.58	$1,139.55	$1,139.50