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	$22.46	13.717%	$25.5408	$25.54	$25.55	$25.50
Purchase #2	$108.85	3.518%	$112.6793	$112.68	$112.70	$112.70
Purchase #3	$213.91	11.537%	$238.5888	$238.59	$238.60	$238.60
Purchase #4	$59.82	13.554%	$67.928	$67.93	$67.95	$67.90
Purchase #5	$31.29	9.745%	$34.3392	$34.34	$34.35	$34.30
Purchase #6	$207.93	11.260%	$231.3429	$231.34	$231.35	$231.30
Purchase #7	$104.48	4.581%	$109.2662	$109.27	$109.25	$109.30
7 purchase totals =	$748.74		$819.6852	$819.69	$819.75	$819.60