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	$166.55	12.584%	$187.5087	$187.51	$187.50	$187.50
Purchase #2	$212.33	3.318%	$219.3751	$219.38	$219.40	$219.40
Purchase #3	$117.47	12.782%	$132.485	$132.49	$132.50	$132.50
Purchase #4	$167.53	9.528%	$183.4923	$183.49	$183.50	$183.50
Purchase #5	$148.58	5.375%	$156.5662	$156.57	$156.55	$156.60
Purchase #6	$162.69	4.620%	$170.2063	$170.21	$170.20	$170.20
Purchase #7	$57.39	3.849%	$59.5989	$59.60	$59.60	$59.60
7 purchase totals =	$1,032.54		$1,109.2325	$1,109.25	$1,109.25	$1,109.30