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	$131.90	12.114%	$147.8784	$147.88	$147.90	$147.90
Purchase #2	$40.45	11.766%	$45.2093	$45.21	$45.20	$45.20
Purchase #3	$127.36	9.808%	$139.8515	$139.85	$139.85	$139.90
Purchase #4	$196.95	12.329%	$221.232	$221.23	$221.25	$221.20
Purchase #5	$173.60	6.731%	$185.285	$185.29	$185.30	$185.30
Purchase #6	$52.92	13.630%	$60.133	$60.13	$60.15	$60.10
Purchase #7	$250.40	10.729%	$277.2654	$277.27	$277.25	$277.30
7 purchase totals =	$973.58		$1,076.8546	$1,076.86	$1,076.90	$1,076.90