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	$132.46	3.735%	$137.4074	$137.41	$137.40	$137.40
Purchase #2	$249.33	10.822%	$276.3125	$276.31	$276.30	$276.30
Purchase #3	$166.96	9.761%	$183.257	$183.26	$183.25	$183.30
Purchase #4	$203.65	3.559%	$210.8979	$210.90	$210.90	$210.90
Purchase #5	$227.68	6.703%	$242.9414	$242.94	$242.95	$242.90
Purchase #6	$100.50	5.428%	$105.9551	$105.96	$105.95	$106.00
Purchase #7	$144.88	13.545%	$164.504	$164.50	$164.50	$164.50
7 purchase totals =	$1,225.46		$1,321.2753	$1,321.28	$1,321.25	$1,321.30