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	$155.39	3.135%	$160.2615	$160.26	$160.25	$160.30
Purchase #2	$175.84	12.610%	$198.0134	$198.01	$198.00	$198.00
Purchase #3	$237.70	12.439%	$267.2675	$267.27	$267.25	$267.30
Purchase #4	$83.93	6.373%	$89.2789	$89.28	$89.30	$89.30
Purchase #5	$236.80	11.592%	$264.2499	$264.25	$264.25	$264.20
Purchase #6	$112.45	5.453%	$118.5819	$118.58	$118.60	$118.60
Purchase #7	$214.59	3.864%	$222.8818	$222.88	$222.90	$222.90
7 purchase totals =	$1,216.70		$1,320.5349	$1,320.53	$1,320.55	$1,320.60