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	$105.42	9.382%	$115.3105	$115.31	$115.30	$115.30
Purchase #2	$229.49	4.342%	$239.4545	$239.45	$239.45	$239.50
Purchase #3	$82.31	12.836%	$92.8753	$92.88	$92.90	$92.90
Purchase #4	$116.25	4.554%	$121.544	$121.54	$121.55	$121.50
Purchase #5	$89.86	11.796%	$100.4599	$100.46	$100.45	$100.50
Purchase #6	$29.32	7.666%	$31.5677	$31.57	$31.55	$31.60
Purchase #7	$75.41	10.464%	$83.3009	$83.30	$83.30	$83.30
7 purchase totals =	$728.06		$784.5128	$784.51	$784.50	$784.60