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	$115.66	13.111%	$130.8242	$130.82	$130.80	$130.80
Purchase #2	$181.50	12.398%	$204.0024	$204.00	$204.00	$204.00
Purchase #3	$18.94	10.236%	$20.8787	$20.88	$20.90	$20.90
Purchase #4	$130.90	9.760%	$143.6758	$143.68	$143.70	$143.70
Purchase #5	$103.78	5.196%	$109.1724	$109.17	$109.15	$109.20
Purchase #6	$196.58	10.836%	$217.8814	$217.88	$217.90	$217.90
Purchase #7	$171.44	7.817%	$184.8415	$184.84	$184.85	$184.80
7 purchase totals =	$918.80		$1,011.2764	$1,011.27	$1,011.30	$1,011.30