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	$76.69	9.377%	$83.8812	$83.88	$83.90	$83.90
Purchase #2	$52.57	7.845%	$56.6941	$56.69	$56.70	$56.70
Purchase #3	$92.80	13.840%	$105.6435	$105.64	$105.65	$105.60
Purchase #4	$193.38	8.209%	$209.2546	$209.25	$209.25	$209.30
Purchase #5	$27.47	9.504%	$30.0807	$30.08	$30.10	$30.10
Purchase #6	$109.39	7.348%	$117.428	$117.43	$117.45	$117.40
Purchase #7	$197.46	12.859%	$222.8514	$222.85	$222.85	$222.90
7 purchase totals =	$749.76		$825.8335	$825.82	$825.90	$825.90