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	$225.70	9.299%	$246.6878	$246.69	$246.70	$246.70
Purchase #2	$52.70	4.142%	$54.8828	$54.88	$54.90	$54.90
Purchase #3	$227.47	12.575%	$256.0744	$256.07	$256.05	$256.10
Purchase #4	$179.95	4.851%	$188.6794	$188.68	$188.70	$188.70
Purchase #5	$78.25	10.317%	$86.3231	$86.32	$86.30	$86.30
Purchase #6	$113.74	10.682%	$125.8897	$125.89	$125.90	$125.90
Purchase #7	$40.31	7.552%	$43.3542	$43.35	$43.35	$43.40
7 purchase totals =	$918.12		$1,001.8914	$1,001.88	$1,001.90	$1,002.00