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	$123.66	10.399%	$136.5194	$136.52	$136.50	$136.50
Purchase #2	$188.69	7.792%	$203.3927	$203.39	$203.40	$203.40
Purchase #3	$200.98	13.193%	$227.4953	$227.50	$227.50	$227.50
Purchase #4	$131.87	5.514%	$139.1413	$139.14	$139.15	$139.10
Purchase #5	$16.46	11.302%	$18.3203	$18.32	$18.30	$18.30
Purchase #6	$10.75	12.642%	$12.109	$12.11	$12.10	$12.10
Purchase #7	$73.71	5.140%	$77.4987	$77.50	$77.50	$77.50
7 purchase totals =	$746.12		$814.4767	$814.48	$814.45	$814.40