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	$62.92	8.528%	$68.2858	$68.29	$68.30	$68.30
Purchase #2	$130.88	9.696%	$143.5701	$143.57	$143.55	$143.60
Purchase #3	$179.41	9.580%	$196.5975	$196.60	$196.60	$196.60
Purchase #4	$111.98	11.777%	$125.1679	$125.17	$125.15	$125.20
Purchase #5	$181.33	10.815%	$200.9408	$200.94	$200.95	$200.90
Purchase #6	$10.38	13.666%	$11.7985	$11.80	$11.80	$11.80
Purchase #7	$76.58	7.524%	$82.3419	$82.34	$82.35	$82.30
7 purchase totals =	$753.48		$828.7025	$828.71	$828.70	$828.70