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	$132.73	11.660%	$148.2063	$148.21	$148.20	$148.20
Purchase #2	$165.47	12.604%	$186.3258	$186.33	$186.35	$186.30
Purchase #3	$139.86	3.192%	$144.3243	$144.32	$144.30	$144.30
Purchase #4	$125.79	8.734%	$136.7765	$136.78	$136.80	$136.80
Purchase #5	$187.31	9.184%	$204.5126	$204.51	$204.50	$204.50
Purchase #6	$113.97	8.405%	$123.5492	$123.55	$123.55	$123.50
Purchase #7	$34.89	8.136%	$37.7287	$37.73	$37.75	$37.70
7 purchase totals =	$900.02		$981.4234	$981.43	$981.45	$981.30