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	$153.43	9.315%	$167.722	$167.72	$167.70	$167.70
Purchase #2	$113.52	13.327%	$128.6488	$128.65	$128.65	$128.60
Purchase #3	$228.56	9.391%	$250.0241	$250.02	$250.00	$250.00
Purchase #4	$215.70	8.865%	$234.8218	$234.82	$234.80	$234.80
Purchase #5	$98.39	13.770%	$111.9383	$111.94	$111.95	$111.90
Purchase #6	$177.48	10.873%	$196.7774	$196.78	$196.80	$196.80
Purchase #7	$7.61	3.178%	$7.8518	$7.85	$7.85	$7.90
7 purchase totals =	$994.69		$1,097.7842	$1,097.78	$1,097.75	$1,097.70