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	$100.46	12.861%	$113.3802	$113.38	$113.40	$113.40
Purchase #2	$200.97	10.505%	$222.0819	$222.08	$222.10	$222.10
Purchase #3	$175.28	12.361%	$196.9464	$196.95	$196.95	$196.90
Purchase #4	$248.35	7.231%	$266.3082	$266.31	$266.30	$266.30
Purchase #5	$113.45	6.416%	$120.729	$120.73	$120.75	$120.70
Purchase #6	$245.56	5.865%	$259.9621	$259.96	$259.95	$260.00
Purchase #7	$205.31	10.575%	$227.0215	$227.02	$227.00	$227.00
7 purchase totals =	$1,289.38		$1,406.4293	$1,406.43	$1,406.45	$1,406.40