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	$140.72	3.629%	$145.8267	$145.83	$145.85	$145.80
Purchase #2	$126.47	12.836%	$142.7037	$142.70	$142.70	$142.70
Purchase #3	$209.98	6.390%	$223.3977	$223.40	$223.40	$223.40
Purchase #4	$146.57	9.547%	$160.563	$160.56	$160.55	$160.60
Purchase #5	$185.42	8.812%	$201.7592	$201.76	$201.75	$201.80
Purchase #6	$61.82	12.553%	$69.5803	$69.58	$69.60	$69.60
Purchase #7	$176.82	13.360%	$200.4432	$200.44	$200.45	$200.40
7 purchase totals =	$1,047.80		$1,144.2738	$1,144.27	$1,144.30	$1,144.30