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	$75.64	3.789%	$78.506	$78.51	$78.50	$78.50
Purchase #2	$72.28	9.296%	$78.9991	$79.00	$79.00	$79.00
Purchase #3	$193.94	8.257%	$209.9536	$209.95	$209.95	$210.00
Purchase #4	$180.55	4.141%	$188.0266	$188.03	$188.05	$188.00
Purchase #5	$182.86	5.377%	$192.6924	$192.69	$192.70	$192.70
Purchase #6	$196.41	4.630%	$205.5038	$205.50	$205.50	$205.50
Purchase #7	$84.63	6.648%	$90.2562	$90.26	$90.25	$90.30
7 purchase totals =	$986.31		$1,043.9377	$1,043.94	$1,043.95	$1,044.00