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	$24.78	4.534%	$25.9035	$25.90	$25.90	$25.90
Purchase #2	$59.54	13.619%	$67.6488	$67.65	$67.65	$67.60
Purchase #3	$92.32	12.361%	$103.7317	$103.73	$103.75	$103.70
Purchase #4	$217.59	8.510%	$236.1069	$236.11	$236.10	$236.10
Purchase #5	$92.25	8.560%	$100.1466	$100.15	$100.15	$100.10
Purchase #6	$231.45	11.662%	$258.4417	$258.44	$258.45	$258.40
Purchase #7	$45.93	9.659%	$50.3664	$50.37	$50.35	$50.40
7 purchase totals =	$763.86		$842.3456	$842.35	$842.35	$842.20