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	$166.67	11.192%	$185.3237	$185.32	$185.30	$185.30
Purchase #2	$17.97	11.502%	$20.0369	$20.04	$20.05	$20.00
Purchase #3	$248.89	12.354%	$279.6379	$279.64	$279.65	$279.60
Purchase #4	$115.73	9.663%	$126.913	$126.91	$126.90	$126.90
Purchase #5	$197.79	8.617%	$214.8336	$214.83	$214.85	$214.80
Purchase #6	$73.35	12.797%	$82.7366	$82.74	$82.75	$82.70
Purchase #7	$125.86	11.178%	$139.9286	$139.93	$139.95	$139.90
7 purchase totals =	$946.26		$1,049.4103	$1,049.41	$1,049.45	$1,049.20