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	$126.31	11.846%	$141.2727	$141.27	$141.25	$141.30
Purchase #2	$213.47	4.388%	$222.8371	$222.84	$222.85	$222.80
Purchase #3	$47.25	9.638%	$51.804	$51.80	$51.80	$51.80
Purchase #4	$41.99	8.488%	$45.5541	$45.55	$45.55	$45.60
Purchase #5	$40.42	3.328%	$41.7652	$41.77	$41.75	$41.80
Purchase #6	$145.27	6.609%	$154.8709	$154.87	$154.85	$154.90
Purchase #7	$156.41	9.459%	$171.2048	$171.20	$171.20	$171.20
7 purchase totals =	$771.12		$829.3088	$829.30	$829.25	$829.40