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	$140.80	3.199%	$145.3042	$145.30	$145.30	$145.30
Purchase #2	$181.88	12.168%	$204.0112	$204.01	$204.00	$204.00
Purchase #3	$106.52	10.139%	$117.3201	$117.32	$117.30	$117.30
Purchase #4	$244.48	4.275%	$254.9315	$254.93	$254.95	$254.90
Purchase #5	$143.65	4.853%	$150.6213	$150.62	$150.60	$150.60
Purchase #6	$131.87	12.829%	$148.7876	$148.79	$148.80	$148.80
Purchase #7	$61.64	6.710%	$65.776	$65.78	$65.80	$65.80
7 purchase totals =	$1,010.84		$1,086.7519	$1,086.75	$1,086.75	$1,086.70