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	$72.28	10.802%	$80.0877	$80.09	$80.10	$80.10
Purchase #2	$85.79	5.478%	$90.4896	$90.49	$90.50	$90.50
Purchase #3	$116.88	12.192%	$131.13	$131.13	$131.15	$131.10
Purchase #4	$106.88	6.602%	$113.9362	$113.94	$113.95	$113.90
Purchase #5	$70.32	5.709%	$74.3346	$74.33	$74.35	$74.30
Purchase #6	$142.66	12.243%	$160.1259	$160.13	$160.15	$160.10
Purchase #7	$186.88	7.404%	$200.7166	$200.72	$200.70	$200.70
7 purchase totals =	$781.69		$850.8206	$850.83	$850.90	$850.70