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	$70.44	11.428%	$78.4899	$78.49	$78.50	$78.50
Purchase #2	$168.62	13.871%	$192.0093	$192.01	$192.00	$192.00
Purchase #3	$239.51	6.730%	$255.629	$255.63	$255.65	$255.60
Purchase #4	$72.63	13.694%	$82.576	$82.58	$82.60	$82.60
Purchase #5	$51.51	7.650%	$55.4505	$55.45	$55.45	$55.50
Purchase #6	$236.60	10.751%	$262.0369	$262.04	$262.05	$262.00
Purchase #7	$7.56	4.223%	$7.8793	$7.88	$7.90	$7.90
7 purchase totals =	$846.87		$934.0709	$934.08	$934.15	$934.10