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	$155.97	10.237%	$171.9366	$171.94	$171.95	$171.90
Purchase #2	$11.93	9.295%	$13.0389	$13.04	$13.05	$13.00
Purchase #3	$185.73	8.159%	$200.8837	$200.88	$200.90	$200.90
Purchase #4	$116.76	12.262%	$131.0771	$131.08	$131.10	$131.10
Purchase #5	$248.51	5.687%	$262.6428	$262.64	$262.65	$262.60
Purchase #6	$125.48	8.714%	$136.4143	$136.41	$136.40	$136.40
Purchase #7	$57.56	9.165%	$62.8354	$62.84	$62.85	$62.80
7 purchase totals =	$901.94		$978.8288	$978.83	$978.90	$978.70