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	$229.48	12.472%	$258.1007	$258.10	$258.10	$258.10
Purchase #2	$218.47	10.476%	$241.3569	$241.36	$241.35	$241.40
Purchase #3	$94.41	9.575%	$103.4498	$103.45	$103.45	$103.40
Purchase #4	$67.71	12.299%	$76.0377	$76.04	$76.05	$76.00
Purchase #5	$145.82	11.307%	$162.3079	$162.31	$162.30	$162.30
Purchase #6	$56.33	3.793%	$58.4666	$58.47	$58.45	$58.50
Purchase #7	$164.39	8.611%	$178.5456	$178.55	$178.55	$178.50
7 purchase totals =	$976.61		$1,078.2652	$1,078.28	$1,078.25	$1,078.20