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	$131.82	4.281%	$137.4632	$137.46	$137.45	$137.50
Purchase #2	$92.57	9.821%	$101.6613	$101.66	$101.65	$101.70
Purchase #3	$155.62	10.697%	$172.2667	$172.27	$172.25	$172.30
Purchase #4	$80.71	12.473%	$90.777	$90.78	$90.80	$90.80
Purchase #5	$101.29	13.405%	$114.8679	$114.87	$114.85	$114.90
Purchase #6	$114.28	5.639%	$120.7242	$120.72	$120.70	$120.70
Purchase #7	$246.90	5.829%	$261.2918	$261.29	$261.30	$261.30
7 purchase totals =	$923.19		$999.0521	$999.05	$999.00	$999.20