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	$49.82	11.506%	$55.5523	$55.55	$55.55	$55.60
Purchase #2	$38.79	3.605%	$40.1884	$40.19	$40.20	$40.20
Purchase #3	$87.70	8.275%	$94.9572	$94.96	$94.95	$95.00
Purchase #4	$38.93	12.678%	$43.8655	$43.87	$43.85	$43.90
Purchase #5	$215.84	3.286%	$222.9325	$222.93	$222.95	$222.90
Purchase #6	$200.52	13.428%	$227.4458	$227.45	$227.45	$227.40
Purchase #7	$99.30	11.656%	$110.8744	$110.87	$110.85	$110.90
7 purchase totals =	$730.90		$795.8161	$795.82	$795.80	$795.90