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	$246.36	13.135%	$278.7194	$278.72	$278.70	$278.70
Purchase #2	$65.50	7.341%	$70.3084	$70.31	$70.30	$70.30
Purchase #3	$231.80	13.119%	$262.2098	$262.21	$262.20	$262.20
Purchase #4	$98.38	13.645%	$111.804	$111.80	$111.80	$111.80
Purchase #5	$125.78	4.687%	$131.6753	$131.68	$131.70	$131.70
Purchase #6	$92.71	13.740%	$105.4484	$105.45	$105.45	$105.40
Purchase #7	$180.81	12.802%	$203.9573	$203.96	$203.95	$204.00
7 purchase totals =	$1,041.34		$1,164.1226	$1,164.13	$1,164.10	$1,164.10