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	$117.79	12.296%	$132.2735	$132.27	$132.25	$132.30
Purchase #2	$156.45	13.195%	$177.0936	$177.09	$177.10	$177.10
Purchase #3	$64.99	11.293%	$72.3293	$72.33	$72.35	$72.30
Purchase #4	$137.74	7.594%	$148.2	$148.20	$148.20	$148.20
Purchase #5	$27.71	11.865%	$30.9978	$31.00	$31.00	$31.00
Purchase #6	$9.84	7.357%	$10.5639	$10.56	$10.55	$10.60
Purchase #7	$79.81	12.594%	$89.8613	$89.86	$89.85	$89.90
7 purchase totals =	$594.33		$661.3194	$661.31	$661.30	$661.40