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	$179.89	5.382%	$189.5717	$189.57	$189.55	$189.60
Purchase #2	$201.92	11.791%	$225.7284	$225.73	$225.75	$225.70
Purchase #3	$122.50	4.333%	$127.8079	$127.81	$127.80	$127.80
Purchase #4	$187.91	10.103%	$206.8945	$206.89	$206.90	$206.90
Purchase #5	$175.72	3.728%	$182.2708	$182.27	$182.25	$182.30
Purchase #6	$161.29	3.871%	$167.5335	$167.53	$167.55	$167.50
Purchase #7	$140.33	11.113%	$155.9249	$155.92	$155.90	$155.90
7 purchase totals =	$1,169.56		$1,255.7317	$1,255.72	$1,255.70	$1,255.70